U.S. patent application number 16/307749 was filed with the patent office on 2019-08-29 for piezoelectric substrate, piezoelectric woven fabric, piezoelectric knitted fabric, piezoelectric device, force sensor, and actua.
This patent application is currently assigned to MITSUI CHEMICALS, INC.. The applicant listed for this patent is MITSUI CHEMICALS, INC., MURATA MANUFACTURING CO., LTD.. Invention is credited to Masamichi ANDO, Shigeo NISHIKAWA, Katsuki ONISHI, Kazuhiro TANIMOTO, Mitsunobu YOSHIDA.
Application Number | 20190267538 16/307749 |
Document ID | / |
Family ID | 60577905 |
Filed Date | 2019-08-29 |
United States Patent
Application |
20190267538 |
Kind Code |
A1 |
YOSHIDA; Mitsunobu ; et
al. |
August 29, 2019 |
PIEZOELECTRIC SUBSTRATE, PIEZOELECTRIC WOVEN FABRIC, PIEZOELECTRIC
KNITTED FABRIC, PIEZOELECTRIC DEVICE, FORCE SENSOR, AND
ACTUATOR
Abstract
The present invention provides: a piezoelectric substrate which
includes a first piezoelectric body having an elongated shape and
helically wound in one direction, and which does not include a core
material, in which the first piezoelectric body includes a helical
chiral polymer (A) having an optical activity; in which the length
direction of the first piezoelectric body is substantially parallel
to the main direction of orientation of the helical chiral polymer
(A) included in the first piezoelectric body; and in which the
first piezoelectric body has a degree of orientation F, as measured
by X-ray diffraction according to the following Equation (a),
within the range of 0.5 or more but less than 1.0: degree of
orientation F=(180.degree.-.alpha.)/180.degree. (a) (in which
.alpha. represents the half-value width of the peak derived from
the orientation).
Inventors: |
YOSHIDA; Mitsunobu;
(Nagoya-shi, Aichi, JP) ; TANIMOTO; Kazuhiro;
(Nagoya-shi, Aichi, JP) ; ONISHI; Katsuki;
(Nagoya-shi, Aichi, JP) ; NISHIKAWA; Shigeo;
(Chiba-shi, Chiba, JP) ; ANDO; Masamichi;
(Nagaokakyo-shi, Kyoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUI CHEMICALS, INC.
MURATA MANUFACTURING CO., LTD. |
Minato-ku, Tokyo
Nagaokakyo-shi, Kyoto |
|
JP
JP |
|
|
Assignee: |
MITSUI CHEMICALS, INC.
Minato-ku, Tokyo
JP
MURATA MANUFACTURING CO., LTD.
Nagaokakyo-shi, Kyoto
JP
|
Family ID: |
60577905 |
Appl. No.: |
16/307749 |
Filed: |
June 5, 2017 |
PCT Filed: |
June 5, 2017 |
PCT NO: |
PCT/JP2017/020886 |
371 Date: |
December 6, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 41/333 20130101;
H01L 41/45 20130101; H01L 41/09 20130101; G01L 1/16 20130101; H01L
41/087 20130101; H01L 41/338 20130101; D01F 6/625 20130101; H01L
41/193 20130101; C08L 67/04 20130101; H01L 41/1132 20130101; H01L
41/113 20130101; H01L 41/082 20130101; H01L 41/312 20130101; H01L
41/33 20130101; C08G 63/08 20130101 |
International
Class: |
H01L 41/193 20060101
H01L041/193; H01L 41/08 20060101 H01L041/08; H01L 41/113 20060101
H01L041/113; D01F 6/62 20060101 D01F006/62 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2016 |
JP |
2016-113011 |
Claims
1. A piezoelectric substrate comprising: (i) a first piezoelectric
body having an elongated shape and helically wound in one
direction, wherein the piezoelectric substrate does not comprise a
core material; or (ii) a first piezoelectric body having an
elongated shape and helically wound in one direction around a core
material; and a non-electrically conductive core material having an
elongated shape, wherein the first piezoelectric body comprises a
helical chiral polymer (A) having optical activity, wherein a
length direction of the first piezoelectric body is substantially
parallel to a main direction of orientation of the helical chiral
polymer (A) included in the first piezoelectric body, and wherein
the first piezoelectric body has a degree of orientation F, as
measured by X-ray diffraction according to the following Equation
(a), within a range of 0.5 or more but less than 1.0: degree of
orientation F=(180.degree.-.alpha.)/180.degree. (a) wherein .alpha.
represents a half-value width of a peak of the orientation.
2. (canceled)
3. The piezoelectric substrate according to claim 1, wherein the
first piezoelectric body is in a fibrous form composed of a single
bundle or a plurality of bundles, and has a major axis diameter of
a cross section of from 0.0001 mm to 10 mm.
4. The piezoelectric substrate according to claim 1, wherein the
first piezoelectric body is in a form of an elongated flat plate
and has a thickness of from 0.001 mm to 0.2 mm and a width of from
0.1 mm to 30 mm, and wherein a ratio of the width of the first
piezoelectric body to the thickness of the first piezoelectric body
is 1.5 or more.
5. The piezoelectric substrate according to claim 1, further
comprising a fiber wound in a direction that is different from the
one direction, wherein the first piezoelectric body and the fiber
are alternately crossed with each other to be formed into a braided
structure.
6. The piezoelectric substrate according to claim 1, further
comprising a second piezoelectric body having an elongated shape
and wound in a direction that is different from the one direction,
wherein the second piezoelectric body comprises a helical chiral
polymer (A) having optical activity, wherein a length direction of
the second piezoelectric body is substantially parallel to a main
direction of orientation of the helical chiral polymer (A) included
in the second piezoelectric body, wherein the second piezoelectric
body has a degree of orientation F, as measured by X-ray
diffraction according to the Equation (a), within the range of 0.5
or more but less than 1.0, wherein the first piezoelectric body and
the second piezoelectric body are alternately crossed with each
other to be formed into a braided structure, and wherein the
helical chiral polymer (A) included in the first piezoelectric body
has a chirality that is different from a chirality of the helical
chiral polymer (A) included in the second piezoelectric body.
7. The piezoelectric substrate according to claim 1, wherein the
first piezoelectric body has a helix angle of from 10.degree. to
80.degree..
8. The piezoelectric substrate according to claim 1, wherein the
core material and the first piezoelectric body are twisted with
each other.
9. The piezoelectric substrate according to claim 8, wherein the
first piezoelectric body is in a fibrous form composed of a single
bundle or a plurality of bundles, and wherein the first
piezoelectric body has a major axis diameter of a cross section of
from 0.0001 mm to 2 mm.
10. The piezoelectric substrate according to claim 1, wherein the
first piezoelectric body comprises an adhesive composition, and
wherein a cured product of the adhesive composition has a tensile
elastic modulus, as measured in accordance with ASTM D-882, of from
0.1 MPa to 10 GPa.
11. The piezoelectric substrate according to claim 1, wherein the
helical chiral polymer (A) included in the first piezoelectric body
is a polylactic acid polymer having a main chain comprising a
repeating unit represented by the following Formula (1):
##STR00005##
12. The piezoelectric substrate according to claim 1, wherein the
helical chiral polymer (A) included in the first piezoelectric body
has an optical purity of 95.00% ee or more.
13. The piezoelectric substrate according to claim 1, wherein the
helical chiral polymer (A) included in the first piezoelectric body
is composed of D-form or L-form.
14. The piezoelectric substrate according to claim 1, wherein a
content of the helical chiral polymer (A) included in the first
piezoelectric body is 80% by mass or more with respect to a total
amount of the first piezoelectric body.
15. A piezoelectric woven fabric having a woven fabric structure
composed of warp threads and weft threads, wherein at least one of
the warp threads or the weft threads comprises the piezoelectric
substrate according to claim 1.
16. A piezoelectric woven fabric having a woven fabric structure
composed of warp threads and weft threads, wherein both of the warp
threads and the weft threads comprise the piezoelectric substrate
according to claim 1, wherein the first piezoelectric body included
in the warp threads is wound in a winding direction that is
different from a winding direction of the first piezoelectric body
included in the weft threads, and wherein the helical chiral
polymer (A) included in the warp threads has a same chirality as a
chirality of the helical chiral polymer (A) included in the weft
threads.
17. A piezoelectric woven fabric having a woven fabric structure
composed of warp threads and weft threads, wherein both of the warp
threads and the weft threads comprise the piezoelectric substrate
according to claim 1, wherein the first piezoelectric body included
in the warp threads is wound in a same winding direction as a
winding direction of the first piezoelectric body included in the
weft threads, and wherein the helical chiral polymer (A) included
in the warp threads has a chirality that is different from a
chirality of the helical chiral polymer (A) included in the weft
threads.
18. A piezoelectric knitted fabric having a knitted fabric
structure comprising the piezoelectric substrate according to claim
1.
19. A piezoelectric device comprising the piezoelectric woven
fabric according to claim 15.
20. A force sensor comprising the piezoelectric substrate according
to claim 1.
21. An actuator comprising the piezoelectric substrate according to
claim 1.
22. A piezoelectric device comprising the piezoelectric knitted
fabric according to claim 18.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a piezoelectric substrate,
a piezoelectric woven fabric, a piezoelectric knitted fabric, a
piezoelectric device, a force sensor, and an actuator.
BACKGROUND ART
[0002] In recent years, the application of piezoelectric bodies
including helical chiral polymers to piezoelectric devices, such as
sensors and actuators, has been investigated. Such piezoelectric
devices include piezoelectric bodies in the form of films.
[0003] The use of polymers having an optical activity, such as
polypeptides and polylactic acid polymers, as the helical chiral
polymers in the piezoelectric bodies has been drawing attention. In
particular, polylactic acid polymers are known to exhibit
piezoelectricity by merely being subjected to mechanical
stretching. It is also known that piezoelectric bodies using
polylactic acid polymers do not require a poling treatment, and
that the piezoelectricity thereof does not decrease over several
years.
[0004] For example, Japanese Patent (JP-B) No. 4934235 and WO
2010/104196 each discloses a piezoelectric body containing a
polylactic acid polymer, which has a high piezoelectric constant
d.sub.14 and an excellent transparency.
[0005] Further, attempts have been made, in recent years, to coat
conductors with materials having piezoelectricity.
[0006] For example, Japanese Patent Application Laid-Open (JP-A)
No. 10-132669 discloses a piezoelectric cable including: a central
conductor; a piezoelectric material layer; an outer conductor; and
a casing; which are disposed coaxially, in this order, from a
center toward an outer periphery of the cable.
[0007] In addition, WO 2014/058077 discloses a piezoelectric unit
in which an electrically conductive fiber is covered with fibers
including a piezoelectric polymer.
SUMMARY OF INVENTION
Technical Problem
[0008] In a case in which a piezoelectric body in the form of a
film (such as the piezoelectric body disclosed in Examples in JP-B
No. 4934235 or WO 2010/104196) is used at a site having large
surface irregularities, or a site which is exposed to large
deformation (for example, when used as a part or the whole of a
wearable product), damage such as breakage or wrinkles may occur in
the piezoelectric body due to deformation, possibly resulting in a
decrease in piezoelectric sensitivity (such as, sensor sensitivity
in the case of using the piezoelectric body as a sensor, or dynamic
sensitivity in the case of using the piezoelectric body as an
actuator; the same shall apply hereinafter).
[0009] Further, JP-A No. 10-132669 discloses the piezoelectric
cable including: a central conductor; a piezoelectric material
layer; an outer conductor; and a casing; which are disposed
coaxially, in this order, from the center toward the outer
periphery of the cable, as described above. It is also disclosed
therein that polyvinylidene fluoride (PVDF) is used as the
piezoelectric material. However, the piezoelectric constant of PVDF
fluctuates over time, and there is a case in which the
piezoelectric constant is decreased with the passing of time. In
addition, PVDF has pyroelectricity due to being a ferroelectric
substance, and thus, fluctuations in piezoelectric signal output
could occur due to temperature changes in the surrounding
environment. Accordingly, in the piezoelectric cable disclosed in
JP-A No. 10-132669, stability of the piezoelectric sensitivity and
stability of the piezoelectric output (stability over time) may be
insufficient. Further, when a load such as repeated bending is
applied to the piezoelectric cable, there is a possibility that a
metal conductor portion thereof may break due to fatigue.
[0010] Further, WO 2014/058077 discloses, as the piezoelectric unit
being covered with fibers including a piezoelectric polymer
(hereinafter, referred to as "piezoelectric fibers"), for example,
a piezoelectric unit in which piezoelectric fibers formed into a
braided tube or a round braid are wound on an electrically
conductive fiber. However, since the directions in which the
piezoelectric fibers are wound with respect to the electrically
conductive fiber are not particularly limited, in the piezoelectric
unit disclosed in WO 2014/058077, in a case in which a tensile
force is applied to the entire braided tube or round braid, and a
shear stress thereby generated in the wound piezoelectric polymer
causes electric charges to be generated in the piezoelectric
polymer, the polarities of the electric charges generated in the
piezoelectric polymer may cancel each other. Accordingly, the
piezoelectric fibers disclosed in WO 2014/058077 may have an
insufficient piezoelectric sensitivity.
[0011] The present disclosure has been done in view of the above
described problems.
[0012] In other words, an object of the present disclosure is to
provide a piezoelectric substrate, a piezoelectric woven fabric, a
piezoelectric knitted fabric, a piezoelectric device, a force
sensor, and an actuator, which have an excellent piezoelectric
sensitivity, an excellent piezoelectric output stability, and an
improved resistance to a load such as repeated bending or to
deformation.
Solution to Problem
[0013] Specific means for achieving the above described object
includes the following embodiments.
<1> A piezoelectric substrate which comprises a first
piezoelectric body having an elongated shape and helically wound in
one direction, and which does not comprise a core material,
[0014] wherein the first piezoelectric body comprises a helical
chiral polymer (A) having optical activity,
[0015] wherein a length direction of the first piezoelectric body
is substantially parallel to a main direction of orientation of the
helical chiral polymer (A) included in the first piezoelectric
body, and
[0016] wherein the first piezoelectric body has a degree of
orientation F, as measured by X-ray diffraction according to the
following Equation (a), within a range of 0.5 or more but less than
1.0:
degree of orientation F=(180.degree.-.alpha.)/180.degree. (a)
[0017] wherein .alpha. represents a half-value width of a peak of
the orientation.
<2> A piezoelectric substrate comprising:
[0018] a core material having an elongated shape; and
[0019] a first piezoelectric body having an elongated shape and
helically wound in one direction around the core material,
[0020] wherein the core material is a non-electrically conductive
core material,
[0021] wherein the first piezoelectric body comprises a helical
chiral polymer (A) having optical activity,
[0022] wherein a length direction of the first piezoelectric body
is substantially parallel to a main direction of orientation of the
helical chiral polymer (A) included in the first piezoelectric
body, and
[0023] wherein the first piezoelectric body has a degree of
orientation F, as measured by X-ray diffraction according to the
following Equation (a), within a range of 0.5 or more but less than
1.0:
degree of orientation F=(180.degree.-.alpha.)/180.degree. (a)
[0024] wherein .alpha. represents a half-value width of a peak of
the orientation.
<3> The piezoelectric substrate according to <1> or
<2>,
[0025] wherein the first piezoelectric body is in a fibrous form
composed of a single bundle or a plurality of bundles, and has a
major axis diameter of a cross section of from 0.0001 mm to 10
mm.
<4> The piezoelectric substrate according to <1> or
<2>,
[0026] wherein the first piezoelectric body is in a form of an
elongated flat plate and has a thickness of from 0.001 mm to 0.2 mm
and a width of from 0.1 mm to 30 mm, and
[0027] wherein a ratio of the width of the first piezoelectric body
to the thickness of the first piezoelectric body is 1.5 or
more.
<5> The piezoelectric substrate according to any one of
<1> to <4>, further comprising a fiber wound in a
direction that is different from the one direction,
[0028] wherein the first piezoelectric body and the fiber are
alternately crossed with each other to be formed into a braided
structure.
<6> The piezoelectric substrate according to any one of
<1> to <4>, further comprising a second piezoelectric
body having an elongated shape and wound in a direction that is
different from the one direction,
[0029] wherein the second piezoelectric body comprises a helical
chiral polymer (A) having optical activity,
[0030] wherein a length direction of the second piezoelectric body
is substantially parallel to a main direction of orientation of the
helical chiral polymer (A) included in the second piezoelectric
body,
[0031] wherein the second piezoelectric body has a degree of
orientation F, as measured by X-ray diffraction according to the
Equation (a), within the range of 0.5 or more but less than
1.0,
[0032] wherein the first piezoelectric body and the second
piezoelectric body are alternately crossed with each other to be
formed into a braided structure, and
[0033] wherein the helical chiral polymer (A) included in the first
piezoelectric body has a chirality that is different from a
chirality of the helical chiral polymer (A) included in the second
piezoelectric body.
<7> The piezoelectric substrate according to any one of
<1> to <6>, wherein the first piezoelectric body has a
helix angle of from 10.degree. to 80.degree.. <8> The
piezoelectric substrate according to <2>, wherein the core
material and the first piezoelectric body are twisted with each
other. <9> The piezoelectric substrate according to
<8>,
[0034] wherein the first piezoelectric body is in a fibrous form
composed of a single bundle or a plurality of bundles, and
[0035] wherein the first piezoelectric body has a major axis
diameter of a cross section of from 0.0001 mm to 2 mm.
<10> The piezoelectric substrate according to any one of
<1> to <9>,
[0036] wherein the first piezoelectric body comprises an adhesive
composition, and
[0037] wherein a cured product of the adhesive composition has a
tensile elastic modulus, as measured in accordance with ASTM D-882,
of from 0.1 MPa to 10 GPa.
<11> The piezoelectric substrate according to any one of
<1> to <10>, wherein the helical chiral polymer (A)
included in the first piezoelectric body is a polylactic acid
polymer having a main chain comprising a repeating unit represented
by the following Formula (1):
##STR00001##
<12> The piezoelectric substrate according to any one of
<1> to <11>, wherein the helical chiral polymer (A)
included in the first piezoelectric body has an optical purity of
95.00% ee or more. <13> The piezoelectric substrate according
to any one of <1> to <12>, wherein the helical chiral
polymer (A) included in the first piezoelectric body is composed of
D-form or L-form. <14> The piezoelectric substrate according
to any one of <1> to <13>, wherein a content of the
helical chiral polymer (A) included in the first piezoelectric body
is 80% by mass or more with respect to a total amount of the first
piezoelectric body. <15> A piezoelectric woven fabric having
a woven fabric structure composed of warp threads and weft
threads,
[0038] wherein at least one of the warp threads or the weft threads
comprises the piezoelectric substrate according to any one of
<1> to <14>.
<16> A piezoelectric woven fabric having a woven fabric
structure composed of warp threads and weft threads,
[0039] wherein both of the warp threads and the weft threads
comprise the piezoelectric substrate according to any one of
<1> to <14>,
[0040] wherein the first piezoelectric body included in the warp
threads is wound in a winding direction that is different from a
winding direction of the first piezoelectric body included in the
weft threads, and
[0041] wherein the helical chiral polymer (A) included in the warp
threads has a same chirality as a chirality of the helical chiral
polymer (A) included in the weft threads.
<17> A piezoelectric woven fabric having a woven fabric
structure composed of warp threads and weft threads,
[0042] wherein both of the warp threads and the weft threads
comprise the piezoelectric substrate according to any one of
<1> to <14>,
[0043] wherein the first piezoelectric body included in the warp
threads is wound in a same winding direction as a winding direction
of the first piezoelectric body included in the weft threads,
and
[0044] wherein the helical chiral polymer (A) included in the warp
threads has a chirality that is different from a chirality of the
helical chiral polymer (A) included in the weft threads.
<18> A piezoelectric knitted fabric having a knitted fabric
structure comprising the piezoelectric substrate according to any
one of <1> to <14>. <19> A piezoelectric device
comprising the piezoelectric woven fabric according to any one of
<15> to <17>, or the piezoelectric knitted fabric
according to <18>. <20> A force sensor including the
piezoelectric substrate according to any one of <1> to
<14>. <21> An actuator including the piezoelectric
substrate according to any one of <1> to <14>.
Advantageous Effects of Invention
[0045] The present disclosure enables to provide a piezoelectric
substrate, a piezoelectric woven fabric, a piezoelectric knitted
fabric, a piezoelectric device, a force sensor, and an actuator,
which have an excellent piezoelectric sensitivity, an excellent
piezoelectric output stability, and an improved resistance to a
load such as repeated bending or to deformation.
BRIEF DESCRIPTION OF DRAWINGS
[0046] FIG. 1 is a side view showing Specific Embodiment A of a
piezoelectric substrate according to a first embodiment.
[0047] FIG. 2 is a side view showing Specific Embodiment B of the
piezoelectric substrate according to the first embodiment.
[0048] FIG. 3 is a side view showing Specific Embodiment C of a
piezoelectric substrate according to a second embodiment.
[0049] FIG. 4 is a side view showing Specific Embodiment D of the
piezoelectric substrate according to the second embodiment.
[0050] FIG. 5 is a side view showing Specific Embodiment E of the
piezoelectric substrate according to the second embodiment.
[0051] FIG. 6 is a schematic diagram showing an example of a
piezoelectric knitted fabric according to a present embodiment.
DESCRIPTION OF EMBODIMENTS
[0052] The embodiments of the present disclosure will now be
described.
[0053] In the present specification, any numerical range indicated
using an expression "from * to" represents a range in which
numerical values described before and after the "to" are included
in the range as a minimum value and a maximum value, respectively.
In a numerical range described in stages, in the present
specification, a lower limit value or an upper limit value
described in a certain numerical range may be replaced with an
upper limit value or a lower limit value in another numerical range
described in stages. Further, in a numerical range described in the
present disclosure, an upper limit value or a lower limit value
described in a certain numerical range may be replaced with a value
shown in Examples.
[0054] In the present specification, the term "main surface" of a
piezoelectric body in the form of an elongated flat plate (a first
piezoelectric body or a second piezoelectric body), refers to each
of both surfaces orthogonal to a thickness direction of the
piezoelectric body in the form of an elongated flat plate (namely,
a surface including the length direction and width direction). The
same applies to the "main surface" of a woven fabric or the "main
surface" of a knitted fabric.
[0055] In the present specification, the term "surface" of a member
refers to the "main surface" of the member, unless otherwise
specified.
[0056] In the present specification, the thickness, width, and
length satisfy the relation: thickness<width<length, as
commonly defined.
[0057] In the present specification, an angle formed between two
line segments is described in a range of from 0.degree. to
90.degree..
[0058] In the present specification, the term "film" is used as a
concept which encompasses not only one generally referred to as a
"film", but also one generally referred to as a "sheet".
[0059] In the present specification, the term "MD direction" refers
to the direction of film flow (Machine Direction), namely a
stretching direction, and the term "TD direction" refers to the
direction orthogonal to the MD direction and parallel to the main
surface of the film (Transverse Direction).
[0060] The first embodiment of the piezoelectric substrate
according to the present disclosure will now be described in
detail.
[0061] [Piezoelectric Substrate according to First Embodiment]
[0062] The piezoelectric substrate according to the first
embodiment includes a first piezoelectric body having an elongated
shape and helically wound in one direction, and does not include a
core material.
[0063] In other words, in the piezoelectric substrate according to
the first embodiment, the first piezoelectric body is helically
wound in one direction with respect to a virtual helical axis, and
not with respect to a core material.
[0064] The term "helical axis" refers to a central axis of a
helical structure formed by the first piezoelectric body.
[0065] Further, the piezoelectric substrate according to the first
embodiment is a piezoelectric substrate wherein the first
piezoelectric body includes a helical chiral polymer (A) having an
optical activity,
[0066] wherein the length direction of the first piezoelectric body
is substantially parallel to the main direction of orientation of
the helical chiral polymer (A) included in the first piezoelectric
body, and
[0067] wherein the first piezoelectric body has a degree of
orientation F, as measured by X-ray diffraction according to the
following Equation (a), within the range of 0.5 or more but less
than 1.0.
Degree of orientation F=(180-.alpha.)/180.degree. (a)
In the Equation (a), .alpha. represents the half-value width of the
peak derived from the orientation. The unit of .alpha. is ".degree.
(degree(s))".
[0068] In the description of the piezoelectric substrate according
to the first embodiment given below, the "first piezoelectric body
having an elongated shape" is sometimes simply referred to as the
"first piezoelectric body". Further, the "virtual helical axis" is
sometimes simply referred to as the "helical axis".
[0069] Examples of the embodiment of the piezoelectric substrate
which does not include a core material include: an embodiment in
which no space (gap), or substantially no space, is present around
the helical axis, in the helical structure formed by the first
piezoelectric body; and an embodiment in which a predetermined
space is present around the helical axis.
[0070] The size of the space present around the helical axis can be
adjusted, for example, by: a method in which the winding method of
the first piezoelectric body is adjusted; a method in which the
first piezoelectric body is wound around a fiber which is soluble
by a specific action (such as a thread soluble in water), under the
above described conditions, followed by allowing the fiber to
dissolve over time, or dissolving and removing the fiber with
water; or a method in which the first piezoelectric body is wound
around a core material, followed by removing the core material. The
major axis diameter of the fiber or the major axis diameter of the
core material can be selected as appropriate depending on the
embodiment of the space. In a case in which the first piezoelectric
body is in the form of an elongated flat plate, the space around
the helical axis can be controlled by increasing or decreasing the
number of windings per 1 m of the first piezoelectric body.
[0071] The degree of orientation F of the first piezoelectric body
is an index indicating the degree of orientation of the helical
chiral polymer (A) included in the first piezoelectric body, and
is, for example, a c-axis orientation degree as measured by a
wide-angle x-ray diffraction apparatus (RINT 2550, manufactured by
Rigaku Corporation; accessory device: rotary sample stand, X-ray
source: CuK.alpha., output: 40 kV 370 mA, detector: scintillation
counter).
[0072] Examples of the method of measuring the degree of
orientation F of the first piezoelectric body are as shown in the
Examples to be described later.
[0073] The term "one direction" refers, when the piezoelectric
substrate according to the first embodiment is seen from one end
side of the helical axis, to the direction in which the first
piezoelectric body is wound from the near side to the far side.
Specifically, the term "one direction" refers to a rightward
direction (wound in a right-handed direction, namely, in the
clockwise direction), or a leftward direction (wound in a
left-handed direction, namely, in the anti-clockwise
direction).
[0074] By having the above configuration, the piezoelectric
substrate according to the first embodiment has an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0075] More specifically, the piezoelectric substrate according to
the first embodiment exhibits piezoelectricity due to the facts
that: the first piezoelectric body includes the helical chiral
polymer (A); the length direction of the first piezoelectric body
is substantially parallel to the main direction of orientation of
the helical chiral polymer (A); and the degree of orientation F of
the first piezoelectric body is 0.5 or more but less than 1.0.
[0076] Further, in the piezoelectric substrate according to the
first embodiment, the disposition of the first piezoelectric body
in the above described arrangement allows a shear force to be
applied to the helical chiral polymer (A), when a tensile force
(stress) is applied in the length direction of the piezoelectric
substrate. As a result, the polarization of the helical chiral
polymer (A) occurs in a radial direction of the piezoelectric
substrate. In a case in which the helically wound, first
piezoelectric body is regarded as an aggregate of micro-regions
which can be roughly considered as a plain in the length direction
of the piezoelectric body, and when the shear force generated due
to the tensile force (stress) in the plain composed of the
micro-regions is applied to the helical chiral polymer, the
direction of the polarization roughly matches the direction of an
electric field generated due to a piezoelectric stress constant
d.sub.14.
[0077] Specifically, for example, in the case of polylactic acid,
such as, in the case of a homopolymer of an L-lactic acid (PLLA)
having a molecular structure in the form of a left-handed helix,
when the first piezoelectric body in which the main direction of
orientation of PLLA is substantially parallel to the length
direction of the piezoelectric body is helically wound in the
left-handed direction with respect to the helical axis to obtain a
structure, and when a tensile force (stress) is applied to the
structure, an outward electric field (polarization) is generated in
a direction parallel to the radial direction, from the center of a
circle of a circular cross section vertical to the tensile force.
Conversely, when the first piezoelectric body in which the main
direction of orientation of PLLA is substantially parallel to the
length direction of the piezoelectric body is helically wound in
the right-handed direction with respect to the helical axis to
obtain a structure, and when a tensile force (stress) is applied to
the structure, an inward electric field (polarization) is generated
in the direction parallel to the radial direction, from the outer
periphery of the circle of the circular cross section vertical to
the tensile force.
[0078] Further, for example, in the case of homopolymer of a
D-lactic acid (PDLA) having a molecular structure in the form of a
right-handed helix, when the first piezoelectric body in which the
main direction of orientation of PDLA is substantially parallel to
the length direction of the piezoelectric body is helically wound
in the left-handed direction with respect to the helical axis to
obtain a structure, and when a tensile force (stress) is applied to
the structure, an inward electric field (polarization) is generated
in the direction parallel to the radial direction, from the outer
periphery of the circle of the circular cross section vertical to
the tensile force. Conversely, when the first piezoelectric body in
which the main direction of orientation of PDLA is substantially
parallel to the length direction of the piezoelectric body is
helically wound in the right-handed direction with respect to the
helical axis to obtain a structure, and when a tensile force
(stress) is applied to the structure, an outward electric field
(polarization) is generated in the direction parallel to the radial
direction, from the center of the circle of the circular cross
section vertical to the tensile force.
[0079] As a result, when a tensile force is applied in the length
direction of the piezoelectric substrate, a potential difference
proportional to the tensile force is generated at respective
portions of the helically disposed first piezoelectric body, in a
phase matched manner, and this is thought to allow for an effective
detection of a voltage signal proportional to the tensile
force.
[0080] Therefore, the piezoelectric substrate according to the
first embodiment has an excellent piezoelectric sensitivity as well
as excellent piezoelectric output stability.
[0081] Further, the piezoelectric substrate according to the first
embodiment has an excellent bendability and flexibility
(ductility), due to including no core material.
[0082] Therefore, the piezoelectric substrate according to the
first embodiment has an improved resistance to a load such as
repeated bending or to deformation.
[0083] In particular, in a piezoelectric substrate in which a
non-pyroelectric polylactic acid polymer is used as the helical
chiral polymer (A), the stability of the piezoelectric sensitivity
and the stability of the piezoelectric output (stability over time)
are further improved as compared to a piezoelectric substrate in
which a pyroelectric PVDF is used.
[0084] In the piezoelectric unit including the piezoelectric fiber
disclosed in the previously described WO 2014/058077, the winding
directions of the piezoelectric fibers with respect to the
electrically conductive fiber are not limited, and in addition, the
origin and the direction of a force as a component of the shear
force are different from those of the piezoelectric substrate
according to the first embodiment, and the piezoelectric substrate
according to the second embodiment to be described later.
Accordingly, the application of a tensile force to the
piezoelectric unit disclosed in WO 2014/058077 does not induce
polarization in the radial direction of the piezoelectric unit; in
other words, polarization does not occur in the direction of the
electric field generated due to the piezoelectric stress constant
d.sub.14. This is thought to result in an insufficient
piezoelectric sensitivity.
[0085] It is to be noted here that the fact that the length
direction of the first piezoelectric body is substantially parallel
to the main direction of orientation of the helical chiral polymer
(A), provides an advantage that the first piezoelectric body has a
high resistance against tension in the length direction (namely,
the piezoelectric body has an excellent tensile strength in the
length direction). This makes the first piezoelectric body less
susceptible to rupture even when the piezoelectric body is
helically wound in one direction with respect to the helical
axis.
[0086] Further, the fact that the length direction of the first
piezoelectric body is substantially parallel to the main direction
of orientation of the helical chiral polymer (A) is also
advantageous, for example, from the viewpoint of productivity in
the case of slitting a stretched piezoelectric film to obtain the
first piezoelectric body (such as a slit ribbon).
[0087] In the present specification, the expression "substantially
parallel" means that the angle formed between two line segments is
0.degree. or more but less than 30.degree. (preferably from
0.degree. to 22.5.degree., more preferably from 0.degree. to
10.degree., still more preferably from 0.degree. to 5.degree., and
particularly preferably from 0.degree. to 3.degree.).
[0088] Further, in the present specification, the "main direction
of orientation of the helical chiral polymer (A)" refers to the
direction in which molecules of the helical chiral polymer (A) are
mainly oriented. The main direction of orientation of the helical
chiral polymer (A) can be confirmed by measuring the degree of
orientation F of the first piezoelectric body.
[0089] In a case in which the first piezoelectric body is produced
by melt spinning raw materials, followed by stretching the
resultant, the main direction of orientation of the helical chiral
polymer (A) in the thus produced first piezoelectric body refers to
a main stretching direction. The main stretching direction refers
to the stretching direction.
[0090] In the same manner, in a case in which the first
piezoelectric body is produced by stretching a film and slitting
the stretched sheet to form a slit, the main direction of
orientation of the helical chiral polymer (A) in the thus produced
first piezoelectric body refers to the main stretching direction.
The main stretching direction as used herein refers to the
stretching direction, in the case of uniaxial stretching; and
refers to a stretching direction having a higher draw ratio, in the
case of biaxial stretching.
[0091] Preferred embodiments of the piezoelectric substrate
according to the first embodiment will be described below.
[0092] In the piezoelectric substrate according to the first
embodiment, it is preferred that the first piezoelectric body is in
a fibrous form composed of a single bundle or a plurality of
bundles, and the major axis diameter of a cross section of the
first piezoelectric body is from 0.0001 mm to 10 mm, more
preferably from 0.001 mm to 5 mm, and still more preferably from
0.002 mm to 1 mm, from the viewpoint of improving the piezoelectric
sensitivity, and the piezoelectric output stability.
[0093] In a case in which a cross section of the first
piezoelectric body (preferably, a fibrous piezoelectric body) has a
circular shape, the "major axis diameter of a cross section" as
used herein refers to the "diameter" of the first piezoelectric
body.
[0094] In a case in which a cross section of the first
piezoelectric body has a deformed shape, the "major axis diameter
of a cross section" refers to the longest width among the widths of
the cross section.
[0095] In a case in which the first piezoelectric body is composed
of a plurality of bundles, the "major axis diameter of a cross
section" refers to the major axis diameter of a cross section of
the piezoelectric body composed of a plurality of bundles.
[0096] It the piezoelectric substrate according to the first
embodiment, the first piezoelectric body is preferably in the form
of an elongated flat plate, from the viewpoint of improving the
piezoelectric sensitivity, and the piezoelectric output
stability.
[0097] Further, it is preferred that the thickness of the first
piezoelectric body is from 0.001 mm to 0.2 mm, the width of the
first piezoelectric body is from 0.1 mm to 30 mm, and the ratio of
the width of the first piezoelectric body to the thickness of the
first piezoelectric body is 1.5 or more.
[0098] A more detailed description will be given below regarding
the size (thickness, width, ratio (width/thickness, length/width))
of the first piezoelectric body in the form of an elongated flat
plate (hereinafter, also referred to as an "elongated flat
plate-like piezoelectric body").
[0099] The thickness of the first piezoelectric body is preferably
from 0.001 mm to 0.2 mm.
[0100] When the thickness is 0.001 mm or more, the strength of the
elongated flat plate-like piezoelectric body can be secured.
Further, the elongated flat plate-like piezoelectric body has an
excellent production suitability.
[0101] When the thickness is 0.2 mm or less, on the other hand, the
degree of freedom of deformation (flexibility) of the elongated
flat plate-like piezoelectric body in the thickness direction is
improved.
[0102] The width of the first piezoelectric body is preferably from
0.1 mm to 30 mm.
[0103] When the width is 0.1 mm or more, the strength of the first
piezoelectric body (elongated flat plate-like piezoelectric body)
can be secured. Further, the elongated flat plate-like
piezoelectric body has an excellent production suitability (for
example, excellent production suitability in a slitting step to be
described later).
[0104] When the width is 30 mm or less, on the other hand, the
degree of freedom of deformation (flexibility) of the elongated
flat plate-like piezoelectric body is improved.
[0105] The ratio of the width of the first piezoelectric body to
the thickness of the first piezoelectric body (hereinafter, also
referred to as the "ratio [width/thickness]") is preferably 1.5 or
more.
[0106] When the ratio [width/thickness] is 1.5 or more, the main
surfaces of the piezoelectric body become evident, and this
facilitates the formation of a charge generation layer oriented
along the length direction of the first piezoelectric body
(elongated flat plate-like piezoelectric body). Further, when the
elongated flat plate-like piezoelectric body is formed into a
piezoelectric woven fabric or a piezoelectric knitted fabric to be
described later, for example, the electric charge generation layers
can be easily oriented on the main surfaces of the resulting
piezoelectric woven fabric or piezoelectric knitted fabric. As a
result, a piezoelectric device (such as a piezoelectric woven
fabric or a piezoelectric knitted fabric) which has an excellent
piezoelectric sensitivity upon measuring a surface potential by a
non-contact surface potentiometer or the like, and which also has
an excellent stability of the piezoelectric sensitivity, is more
easily obtained.
[0107] The width of the first piezoelectric body is more preferably
from 0.5 mm to 15 mm.
[0108] When the width is 0.5 mm or more, the strength of the first
piezoelectric body (elongated flat plate-like piezoelectric body)
is further improved. In addition, the twisting of the elongated
flat plate-like piezoelectric body can be further prevented,
thereby further improving the piezoelectric sensitivity and the
stability thereof.
[0109] When the width is 15 mm or less, the degree of freedom of
deformation (flexibility) of the elongated flat plate-like
piezoelectric body is further improved.
[0110] In the first piezoelectric body, the ratio of the length to
the width (hereinafter, also referred to as the ratio
[length/width]) is preferably 10 or more.
[0111] When the ratio [length/width] is 10 or more, the degree of
freedom of deformation (flexibility) of the first piezoelectric
body (elongated flat plate-like piezoelectric body) is further
improved. In addition, it becomes possible to impart
piezoelectricity over a wider area, in a piezoelectric device (such
as a piezoelectric woven fabric or a piezoelectric knitted fabric)
in which the elongated flat plate-like piezoelectric body is
used.
[0112] In the piezoelectric substrate according to the first
embodiment, it is preferred that the piezoelectric substrate
further includes a fiber wound in a direction different from the
one direction, and that the first piezoelectric body and the fiber
are alternately crossed with each other to be formed into a braided
structure.
[0113] This arrangement allows a state in which the first
piezoelectric body is wound in one direction with respect to the
helical axis, to be more easily retained, when the piezoelectric
substrate is bent and deformed. As a result, polarization is more
likely to occur in the helical chiral polymer (A) included in the
first piezoelectric body, when a tensile force is applied in the
length direction of the piezoelectric substrate. Note that, in the
braided structure of this embodiment, it is preferred that there is
no gap between the first piezoelectric body and the fiber, in order
to allow for a more efficient application of a tensile force to the
first piezoelectric body.
[0114] In the piezoelectric substrate according to the first
embodiment, it is preferred that:
[0115] the piezoelectric substrate further includes a second
piezoelectric body having an elongated shape and wound in a
direction different from the one direction;
[0116] the second piezoelectric body includes a helical chiral
polymer (A) having an optical activity;
[0117] the length direction of the second piezoelectric body is
substantially parallel to the main direction of orientation of the
helical chiral polymer (A) included in the second piezoelectric
body;
[0118] the second piezoelectric body has a degree of orientation F,
as measured by X-ray diffraction according to the Equation (a),
within the range of 0.5 or more but less than 1.0;
[0119] the first piezoelectric body and the second piezoelectric
body are alternately crossed with each other to be formed into a
braided structure; and
[0120] the helical chiral polymer (A) included in the first
piezoelectric body has a chirality different from the chirality of
the helical chiral polymer (A) included in the second piezoelectric
body.
[0121] By this arrangement, polarization occurs in both the helical
chiral polymer (A) included in the first piezoelectric body and the
helical chiral polymer (A) included in the second piezoelectric
body, when a tensile force is applied in the length direction of
the piezoelectric substrate, for example. The polarization of each
of the helical chiral polymers (A) occurs in the radial direction
of the piezoelectric substrate.
[0122] This allows for a more effective detection of the voltage
signal proportional to the tensile force. As a result, the
piezoelectric sensitivity, and the piezoelectric output stability
are further improved.
[0123] Further, the piezoelectric substrate according to the first
embodiment is a piezoelectric substrate having an excellent
bendability and flexibility (ductility) due to including no core
material, as described above.
[0124] In addition, in a case in which the piezoelectric substrate
according to the first embodiment includes the first piezoelectric
body and the second piezoelectric body which are formed into a
braided structure, adequate gaps are formed between the first
piezoelectric body and second piezoelectric body. As a result, when
a force which causes the piezoelectric substrate to be bent and
deformed is applied thereto, the gaps absorb the deformation,
allowing the piezoelectric substrate to be flexibly bent and
deformed.
[0125] Accordingly, the piezoelectric substrate according to the
first embodiment can be suitably used as a constituent member in a
product which needs to conform to a three-dimensional plane, for
example, a wearable product (such as a piezoelectric woven fabric,
a piezoelectric knitted fabric, a piezoelectric device, a force
sensor, or a device for obtaining biological information, to be
described later).
[0126] In the piezoelectric substrate according to the first
embodiment, it is preferred that the first piezoelectric body has a
helix angle of from 10.degree. to 80.degree.
(45.degree..+-.35.degree.), more preferably from 15.degree. to
75.degree. (45.degree..+-.30.degree.), and still more preferably
from 35.degree. to 65.degree. (45.degree..+-.10.degree.), from the
viewpoint of improving the piezoelectric sensitivity, and the
piezoelectric output stability.
[0127] The term "helix angle" refers to the angle formed between
the helical axis and an arrangement direction of the first
piezoelectric body with respect to the helical axis.
[0128] In the piezoelectric substrate according to the first
embodiment, it is preferred that:
[0129] the first piezoelectric body includes an adhesive
composition, and
[0130] a cured product of the adhesive composition has a tensile
elastic modulus, as measured in accordance with ASTM D-882, of from
0.1 MPa to 10 GPa, more preferably from 0.1 MPa to 5 GPa, and still
more preferably from 0.1 MPa to 3 GPa.
[0131] This arrangement allows adjacent portions of the first
piezoelectric body to be adhered with each other by the adhesive
composition (adhesive), and makes the relative positions of the
portions of the first piezoelectric body less likely to be
displaced. Consequently, a tensile force is more efficiently
applied to the first piezoelectric body, allowing a shear stress to
be more effectively applied to the helical chiral polymer (A)
included in the first piezoelectric body. As a result, a voltage
signal (electric charge signal) proportional to the tensile force
can be effectively detected.
[0132] When the tensile elastic modulus of the cured product of the
adhesive is 0.1 MPa or more, a strain (piezoelectric strain) caused
by the tensile force applied to the piezoelectric substrate
according to the first embodiment is less likely to be alleviated
at adhesive portions, as a result of which the efficiency of
transmitting the strain to the first piezoelectric body is
enhanced.
[0133] Accordingly, the piezoelectric sensitivity, and the
piezoelectric output stability are further improved.
[0134] The tensile elastic modulus after bonding, of the adhesive
in the first embodiment, namely, the tensile elastic modulus of the
cured product of the adhesive, is preferably about equal to or
greater than the tensile elastic modulus of the first piezoelectric
body.
[0135] The method of measuring the tensile elastic modulus of the
cured product of the adhesive composition will be described in
detail in the Examples.
[0136] In the piezoelectric substrate according to the first
embodiment, the helical chiral polymer (A) included in the first
piezoelectric body is preferably a polylactic acid polymer having a
main chain including a repeating unit represented by the following
Formula (1), from the viewpoint of further improving the
piezoelectricity.
##STR00002##
[0137] In the piezoelectric substrate according to the first
embodiment, the helical chiral polymer (A) included in the first
piezoelectric body preferably has an optical purity of 95.00% ee or
more, from the viewpoint of further improving the
piezoelectricity.
[0138] In the piezoelectric substrate according to the first
embodiment, the helical chiral polymer (A) included in the first
piezoelectric body is preferably composed of D-form or L-form from
the viewpoint of further improving the piezoelectricity.
[0139] In the piezoelectric substrate according to the first
embodiment, the content of the helical chiral polymer (A) included
in the first piezoelectric body is preferably 80% by mass or more
with respect to the total amount of the first piezoelectric body,
from the viewpoint of further improving the piezoelectricity.
[0140] Specific Embodiment A of the piezoelectric substrate
according to the first embodiment will be described below, with
reference to the drawings.
[0141] [Specific Embodiment A]
[0142] FIG. 1 is a side view showing Specific Embodiment A of the
piezoelectric substrate according to the first embodiment.
[0143] As shown in FIG. 1, a piezoelectric substrate 10 of Specific
Embodiment A includes a first piezoelectric body 14A having an
elongated shape, and does not include a core material.
[0144] The first piezoelectric body 14A is helically wound in one
direction with respect to a helical axis G1 at a helix angle
.beta.1, from one end to the other, such that no gap is formed and
no space is present around the helical axis G1. Further, the first
piezoelectric body 14A is impregnated with an adhesive (not shown
in the figure), and adjacent portions of the first piezoelectric
body 14A are adhered with each other by the adhesive.
[0145] The "helix angle .beta.1" refers to the angle formed between
the helical axis G1, and the arrangement direction of the first
piezoelectric body 14A with respect to the helical axis G1.
[0146] Further, in Specific Embodiment A, the first piezoelectric
body 14A is wound in the left-handed direction with respect to the
helical axis G1. Specifically, when the piezoelectric substrate 10
is seen from one end side of the helical axis G1 (on the right
side, in the case of FIG. 1), the first piezoelectric body 14A is
wound in the left-handed direction, from the near side to the far
side.
[0147] Further, in FIG. 1, the main direction of orientation of the
helical chiral polymer (A) included in the first piezoelectric body
14A is shown with a two-way arrow E1. In other words, the main
direction of orientation of the helical chiral polymer (A) is
substantially parallel to the arrangement direction (the length
direction of the first piezoelectric body 14A) of the first
piezoelectric body 14A.
[0148] The functions of the piezoelectric substrate 10 of Specific
Embodiment A will be described below.
[0149] For example, when a tensile force is applied in the length
direction of the piezoelectric substrate 10, a shear force is
applied to the helical chiral polymer (A) included in the first
piezoelectric body 14A, and polarization occurs in the helical
chiral polymer (A). The polarization of the helical chiral polymer
(A) occurs in the radial direction of the piezoelectric substrate
10, and it is thought that the polarization occurs in that
direction in a phase matched manner. This allows for an effective
detection of a voltage signal proportional to the tensile
force.
[0150] Further, in the piezoelectric substrate 10, since the first
piezoelectric body 14A is impregnated with an adhesive (not shown
in the figure), as described above, the relative positions of the
portions of the first piezoelectric body 14A are less likely to be
displaced, allowing a tensile force to be more effectively applied
to the first piezoelectric body 14A.
[0151] In addition, the piezoelectric substrate 10 has an excellent
bendability and flexibility, due to including no core material.
[0152] The above described arrangements allow the piezoelectric
substrate 10 of Specific Embodiment A to have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0153] Next, Specific Embodiments B1 and B2 of the piezoelectric
substrates according to the first embodiment will be described with
reference to the drawings. In the description given below, the
repetition of the description given in Specific Embodiment A will
be omitted.
[0154] [Specific Embodiment B1]
[0155] FIG. 2 is a side view showing Specific Embodiment B1 of the
piezoelectric substrate according to the first embodiment.
[0156] A piezoelectric substrate 10A of Specific Embodiment B1
includes the first piezoelectric body 14A, and a second
piezoelectric body 14B, and does not include a core material. The
first piezoelectric body 14A and the second piezoelectric body 14B
are alternately crossed with each other to be formed into a braided
structure.
[0157] The helical chiral polymer (A) included in the first
piezoelectric body 14A has a chirality different from the chirality
of the helical chiral polymer (A) included in the second
piezoelectric body 14B.
[0158] As shown in FIG. 2, in the piezoelectric substrate 10A of
Specific Embodiment B1, the first piezoelectric body 14A is
helically wound in the left-handed direction with respect to a
helical axis G2 at the helix angle .beta.1, and the second
piezoelectric body 14B is helically wound in the right-handed
direction at a helix angle .beta.2, and in addition, the first
piezoelectric body 14A and the second piezoelectric body 14B are
alternately crossed with each other.
[0159] Further, in the braided structure shown in FIG. 2, the main
direction of orientation (two-way arrow E1) of the helical chiral
polymer (A) included in the first piezoelectric body 14A is
substantially parallel to the arrangement direction of the first
piezoelectric body 14A. In the same manner, the main direction of
orientation (two-way arrow E2) of the helical chiral polymer (A)
included in the second piezoelectric body 14B is substantially
parallel to the arrangement direction of the second piezoelectric
body 14B.
[0160] The functions of the piezoelectric substrate 10A of Specific
Embodiment B1 will be described below.
[0161] For example, when a tensile force is applied in the length
direction of the piezoelectric substrate 10A, polarization occurs
in both the helical chiral polymer (A) included in the first
piezoelectric body 14A, and the helical chiral polymer (A) included
in the second piezoelectric body 14B. The polarization of each of
the helical chiral polymers (A) occurs in the radial direction of
the piezoelectric substrate 10A. This allows for an effective
detection of a voltage signal proportional to the tensile
force.
[0162] Further, the piezoelectric substrate 10A has an excellent
bendability and flexibility, due to having a braided structure with
no core material.
[0163] The above described arrangements allow the piezoelectric
substrate 10A of Specific Embodiment B1 to have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0164] In particular, in the piezoelectric substrate 10A of
Specific Embodiment B1, when a tensile force is applied to the
length direction of the piezoelectric substrate 10A, a shear stress
is applied to the first piezoelectric body 14A wound in the
left-handed direction and the second piezoelectric body 14B wound
in the right-handed direction, which are formed into the braided
structure, and the direction of polarization in the first
piezoelectric body 14A matches the direction of polarization in the
second piezoelectric body 14B. This causes an increase in volume
fractions contributing to the piezoelectric performance in the
first piezoelectric body 14A and the second piezoelectric body 14B,
thereby further improving the piezoelectric performance.
Accordingly, the piezoelectric substrate 10A of Specific Embodiment
B1 can be suitably used as a constituent member in a product which
needs to conform to a three-dimensional plane, for example, a
wearable product (such as a piezoelectric woven fabric, a
piezoelectric knitted fabric, a piezoelectric device, a force
sensor, or a device for obtaining biological information, to be
described later).
[0165] [Specific Embodiment B2]
[0166] The piezoelectric substrate of Specific Embodiment B2 has
the same configuration as the piezoelectric substrate 10A of
Specific Embodiment B1, except for including a fiber instead of the
second piezoelectric body 14B in the piezoelectric substrate 10A of
Specific Embodiment B1 shown in FIG. 2. In other words, the
piezoelectric substrate of Specific Embodiment B2 includes the
first piezoelectric body and the fiber, and does not include a core
material, wherein the first piezoelectric body and the fiber are
alternately crossed with each other to be formed into a braided
structure. The fiber in Specific Embodiment B2 is a fiber which
does not have piezoelectricity. In the case of this embodiment, the
winding direction of the fiber may be right-handed or
left-handed.
[0167] In Specific Embodiment B2, when the piezoelectric substrate
is bent and deformed, the state in which the first piezoelectric
body is wound in one direction with respect to the helical axis is
more easily retained. This facilitates the occurrence of
polarization in the helical chiral polymer (A) included in the
first piezoelectric body, when a tensile force is applied in the
length direction of the piezoelectric substrate.
[0168] Further, the piezoelectric substrate of Specific Embodiment
B2 has an excellent bendability and flexibility, due to having a
braided structure with no core material.
[0169] The above described arrangements allow the piezoelectric
substrate of Specific Embodiment B2 to also have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0170] Next, materials and the like included in the piezoelectric
substrate according to the first embodiment will be described.
[0171] <First Piezoelectric Body>
[0172] The piezoelectric substrate according to the first
embodiment includes a first piezoelectric body having an elongated
shape.
[0173] The first piezoelectric body is a piezoelectric body
including a helical chiral polymer (A) having an optical
activity.
[0174] (Helical Chiral Polymer (A))
[0175] The first piezoelectric body in the first embodiment
includes a helical chiral polymer (A) having an optical
activity.
[0176] The "helical chiral polymer (A) having an optical activity"
as used herein refers to a polymer having a molecular structure in
the form of a helix and having a molecular optical activity.
[0177] Examples of the helical chiral polymer (A) include
polypeptides, cellulose derivatives, polylactic acid polymers,
polypropylene oxide, and poly(.beta.-hydroxybutyric acid).
[0178] Examples of the polypeptide include poly(.gamma.-benzyl
glutarate), and poly(.gamma.-methyl glutarate).
[0179] Examples of the cellulose derivative include cellulose
acetate, and cyanoethyl cellulose.
[0180] The helical chiral polymer (A) preferably has an optical
purity of 95.00% ee or more, more preferably 96.00% ee or more,
still more preferably 99.00% ee or more, and further still more
preferably 99.99% ee or more, from the viewpoint of improving the
piezoelectricity of the first piezoelectric body. The optical
purity of the helical chiral polymer (A) is desirably 100.00% ee.
When the optical purity of the helical chiral polymer (A) is within
the above range, packing of polymer crystals exhibiting
piezoelectricity becomes denser, resulting in an enhanced
piezoelectricity.
[0181] The optical purity of the helical chiral polymer (A) as used
herein refers to a value calculated by the following Equation:
Optical purity (% ee)=100.times.|amount of L-form-amount of
D-form|/(amount of L-form+amount of D-form)
[0182] In other words, the optical purity of the helical chiral
polymer (A) is defined as: {a numerical value obtained by dividing
"the difference (absolute value) between the amount of L-form [% by
mass] of the helical chiral polymer (A) and the amount of D-form [%
by mass] of the helical chiral polymer (A)" by "the total amount of
the amount of L-form [% by mass] of the helical chiral polymer (A)
and the amount of D-form [% by mass] of the helical chiral polymer
(A)"}, multiplied by {100}.
[0183] As the values of the amount of L-form [% by mass] of the
helical chiral polymer (A) and the amount of D-form [% by mass] of
the helical chiral polymer (A), values obtained by a method using
high performance liquid chromatography (HPLC) are used. Specific
details of the measurement will be described later.
[0184] The helical chiral polymer (A) is preferably a polymer
having a main chain including a repeating unit represented by the
following Formula (1), from the viewpoint of increasing the optical
purity and improving the piezoelectricity.
##STR00003##
[0185] Examples of the polymer having a main chain including a
repeating unit represented by the following Formula (1) include a
polylactic acid polymer.
[0186] The "polylactic acid polymer" as used herein refers to
"polylactic acid (a polymer consisting of repeating units derived
from a monomer selected from L-lactic acid or D-lactic acid)", a
"copolymer of L-lactic acid or D-lactic acid and a compound
copolymerizable with the L-lactic acid or the D-lactic acid", or a
mixture of both.
[0187] Among the polylactic acid polymers, polylactic acid is
preferred, and a homopolymer of L-lactic acid (PLLA, also simply
referred to as "L-form") or a homopolymer of D-lactic acid (PDLA,
also simply referred to as "D-form") is most preferred.
[0188] Polylactic acid is a polymer having a long chain structure
formed by polymerization of lactic acid via ester bonds.
[0189] It is known that polylactic acid can be formed by: a lactide
method in which lactide is produced as an intermediate; a direct
polymerization method in which lactic acid is heated in a solvent
under reduced pressure, followed by polymerization while removing
water; or the like.
[0190] Examples of the polylactic acid include: a homopolymer of
L-lactic acid; a homopolymer of D-lactic acid; a block copolymer
containing a polymer of at least one of L-lactic acid or D-lactic
acid; and a graft copolymer containing a polymer of at least one of
L-lactic acid or D-lactic acid.
[0191] Examples of the "compound copolymerizable with L-lactic acid
or D-lactic acid" include: hydroxycarboxylic acids such as glycolic
acid, dimethyl glycolic acid, 3-hydroxybutyric acid,
4-hydroxybutyric acid, 2-hydroxypropanoic acid, 3-hydroxypropanoic
acid, 2-hydroxyvaleric acid, 3-hydroxyvaleric acid,
4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 2-hydroxycaproic
acid, 3-hydroxycaproic acid, 4-hydroxycaproic acid,
5-hydroxycaproic acid, 6-hydroxycaproic acid,
6-hydroxymethylcaproic acid, and mandelic acid; cyclic esters such
as glycolide, .beta.-methyl-.delta.-valerolactone,
.gamma.-valerolactone, and .epsilon.-caprolactone; polyvalent
carboxylic acids such as oxalic acid, malonic acid, succinic acid,
glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic
acid, undecanedioic acid, dodecanedioic acid, and terephthalic
acid, and anhydrides thereof; polyhydric alcohols such as ethylene
glycol, diethylene glycol, triethylene glycol, 1,2-propanediol,
1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol,
1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol,
3-methyl-1,5-pentanediol, neopentyl glycol, tetramethylene glycol,
and 1,4-hexanedimethanol; polysaccharides such as cellulose; and
aminocarboxylic acids such as .alpha.-amino acid.
[0192] Examples of the "copolymer of L-lactic acid or D-lactic acid
and a compound copolymerizable with the L-lactic acid or the
D-lactic acid" include block copolymers and graft copolymers having
a polylactic acid sequence capable of forming a helical
crystal.
[0193] Further, the concentration of a structure derived from a
copolymer component in the helical chiral polymer (A) is preferably
20 mol % or less.
[0194] For example, in a case in which the helical chiral polymer
(A) is a polylactic acid polymer, the concentration of the
structure derived from the copolymer component is preferably 20 mol
% or less, with respect to the total number of moles of a structure
derived from lactic acid and the structure derived from the
compound (copolymer component) copolymerizable with lactic acid, in
the polylactic acid polymer.
[0195] The polylactic acid polymer can be produced, for example,
by: the method disclosed in JP-A No. 59-096123 or JP-A No.
7-033861, in which lactic acid is directly subjected to dehydration
condensation; the method disclosed in U.S. Pat. Nos. 2,668,182,
4,057,357, or the like, in which ring-opening polymerization is
carried out using lactide, which is a cyclic dimer of lactic acid;
or the like.
[0196] In order to control the optical purity of the polylactic
acid polymer obtained by any of the above described production
methods to 95.00% ee or more, and in the case of producing
polylactic acid by the lactide method, for example, it is preferred
to carry out polymerization of lactide whose optical purity has
been increased to 95.00% ee or more by a crystallization
operation.
[0197] -Weight Average Molecular Weight--
[0198] The helical chiral polymer (A) preferably has a weight
average molecular weight (Mw) of 50,000 to one million.
[0199] When the helical chiral polymer (A) has an Mw of 50,000 or
more, the first piezoelectric body has an improved mechanical
strength. The Mw is preferably 100,000 or more, and more preferably
200,000 or more.
[0200] When the helical chiral polymer (A) has an Mw of one million
or less, on the other hand, the moldability in the case of
obtaining the first piezoelectric body by molding (such as
extrusion molding or melt spinning) is improved. The Mw is
preferably 800,000 or less, and more preferably 300,000 or
less.
[0201] Further, the helical chiral polymer (A) preferably has a
molecular weight distribution (Mw/Mn) of from 1.1 to 5, and more
preferably from 1.2 to 4, from the viewpoint of improving the
strength of the first piezoelectric body. The molecular weight
distribution is still more preferably from 1.4 to 3.
[0202] Each of the weight average molecular weight (Mw) and the
molecular weight distribution (Mw/Mn) of the helical chiral polymer
(A) refers to a value measured by gel permeation chromatography
(GPC). The Mn as used herein is a number average molecular weight
of the helical chiral polymer (A).
[0203] An example of the method of measuring the Mw and Mw/Mn of
the helical chiral polymer (A) by GPC will be shown below.
[0204] -GPC Measuring Apparatus--
[0205] GPC-100, manufactured by Waters Corporation
[0206] -Column--
[0207] SHODEX LF-804, manufactured by Showa Denko K.K.
[0208] -Preparation of Sample--
[0209] The first piezoelectric body is dissolved in a solvent (such
as chloroform) at 40.degree. C. to prepare a sample solution having
a concentration of 1 mg/ml.
[0210] -Measurement Conditions--
[0211] A quantity of 0.1 ml of the sample solution prepared with a
solvent [chloroform] is introduced into the column, at a
temperature of 40.degree. C., and at a flow velocity of 1
ml/min.
[0212] The concentration of the sample in the sample solution,
which has been separated by the column, is measured by a
differential refractometer.
[0213] A universal calibration curve is prepared using a
polystyrene standard sample, to calculate the weight average
molecular weight (Mw) and the molecular weight distribution (Mw/Mn)
of the helical chiral polymer (A).
[0214] A commercially available polylactic acid can be used as a
polylactic acid polymer, which is an example of the helical chiral
polymer (A).
[0215] Examples of commercially available products thereof include:
PURASORB (PD, PL), manufactured by PURAC Biomaterials; LACEA
(H-100, H-400), manufactured by Mitsui Chemicals, Inc.; and INGEO
(trade mark) biopolymer, manufactured by NatureWorks LLC.
[0216] In the case of using a polylactic acid polymer as the
helical chiral polymer (A), and in order to control the weight
average molecular weight (Mw) of the polylactic acid polymer to
50,000 or more, it is preferred that the polylactic acid polymer is
produced by the lactide method or the direct polymerization
method.
[0217] The first piezoelectric body in the first embodiment may
include one kind of the above described helical chiral polymer (A),
or two or more kinds thereof.
[0218] The content of the helical chiral polymer (A) (the total
content, in cases where two or more kinds thereof are included) in
the first piezoelectric body in the first embodiment is preferably
80% by mass or more with respect to the total amount of the first
piezoelectric body.
[0219] (Stabilizer)
[0220] It is preferred that the first piezoelectric body in the
first embodiment further includes a stabilizer (B) containing one
or more functional groups selected from the group consisting of
carbodiimide group, epoxy group, and isocyanate group, within one
molecule, and having a weight average molecular weight of from 200
to 60,000. This allows for further improving resistance to moist
heat.
[0221] As the stabilizer (B), it is possible to use the "stabilizer
(B)" described in paragraphs 0039 to 0055 in WO 2013/054918.
[0222] Examples of a compound (carbodiimide compound) which
contains a carbodiimide group within one molecule and which can be
used as the stabilizer (B) include a monocarbodiimide compound, a
polycarbodiimide compound, and a cyclic carbodiimide compound.
[0223] As the monocarbodiimide compound, dicyclohexyl carbodiimide,
bis-2,6-diisopropylphenyl carbodiimide or the like can be suitably
used.
[0224] As the polycarbodiimide compound, one prepared by any of
various kinds of methods can be used. It is possible to use a
polycarbodiimide compound prepared by a conventional method of
producing a polycarbodiimide (such as the method described in U.S.
Pat. No. 2,941,956, JP-B No. S47-33279, J. Org. Chem. 28, 2069 to
2075 (1963), or Chemical Review 1981, Vol. 81, No. 4, p 619 to
621). Specifically, a carbodiimide compound disclosed in JP-B No.
4084953 can also be used.
[0225] Examples of the polycarbodiimide compound include [0226]
poly(4,4'-dicyclohexylmethanecarbodiimide), [0227]
poly(N,N'-di-2,6-diisopropylphenylcarbodiimide), and [0228]
poly(1,3,5-triisopropylphenylene-2,4-carbodiimide).
[0229] The cyclic carbodiimide compound can be synthesized
according to the method described in JP-A No. 2011-256337, or the
like.
[0230] The carbodiimide compound may be a commercially available
product, and examples thereof include: B2756 (trade name),
manufactured by Tokyo Chemical Industry Co., Ltd.; CARBODILITE LA-1
(trade name), manufactured by Nisshinbo Chemical Inc.; STABAXOL P,
STABAXOL P400 and STABAXOL I (all of these are trade names)
manufactured by Rhein Chemie Rheinau GmbH.
[0231] Examples of a compound (isocyanate compound) which contains
an isocyanate group within one molecule and which can be used as
the stabilizer (B) include 3-(triethoxysilyl)propyl isocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene
diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane
diisocyanate, 2,4'-diphenylmethane diisocyanate,
2,2'-diphenylmethane diisocyanate, xylylene diisocyanate,
hydrogenated xylylene diisocyanate, and isophorone
diisocyanate.
[0232] Examples of a compound (epoxy compound) which contains an
epoxy group within one molecule and which can be used as the
stabilizer (B) include phenyl glycidyl ether, diethylene glycol
diglycidyl ether, bisphenol A-diglycidyl ether, hydrogenated
bisphenol A-diglycidyl ether, phenol novolac type epoxy resin,
cresol novolac type epoxy resin, and epoxidized polybutadiene.
[0233] The weight average molecular weight of the stabilizer (B) is
from 200 to 60,000, as described above, but more preferably from
200 to 30,000, and still more preferably from 300 to 18,000.
[0234] Having a molecular weight within the above range facilitates
the movement of the stabilizer (B), and an effect of improving the
resistance to moist heat will be more effectively exhibited.
[0235] It is particularly preferred that the stabilizer (B) has a
weight average molecular weight of from 200 to 900. A weight
average molecular weight of from 200 to 900 roughly corresponds
with a number average molecular weight of from 200 to 900. Further,
when the weight average molecular weight is from 200 to 900, there
is a case in which the molecular weight distribution is 1.0, and in
this case, the "weight average molecular weight of from 200 to 900"
can be simply referred to as a "molecular weight of from 200 to
900".
[0236] In a case in which the first piezoelectric body in the first
embodiment includes the stabilizer (B), the first piezoelectric
body may include only one kind of the stabilizer (B), or two or
more kinds thereof.
[0237] In a case in which the first piezoelectric body in the first
embodiment includes the stabilizer (B), the content of the
stabilizer (B) is preferably from 0.01 parts by mass to 10 parts by
mass, more preferably from 0.01 parts by mass to 5 parts by mass,
still more preferably from 0.1 parts by mass to 3 parts by mass,
and particularly preferably from 0.5 parts by mass to 2 parts by
mass, with respect to 100 parts by mass of the helical chiral
polymer (A).
[0238] When the content of the stabilizer (B) is 0.01 parts by mass
or more, the resistance to moist heat will be further improved.
[0239] When the content of the stabilizer (B) is 10 parts by mass
or less, on the other hand, a decrease in the transparency can be
further prevented.
[0240] Examples of preferred embodiments of the stabilizer (B)
include an embodiment in which a stabilizer (B1) containing one or
more functional groups selected from the group consisting of
carbodiimide group, epoxy group, and isocyanate group, and having a
number average molecular weight of from 200 to 900, and a
stabilizer (B2) containing two or more of the one or more
functional groups selected from the group consisting of
carbodiimide group, epoxy group, and isocyanate group within one
molecule, and having a number average molecular weight of from
1,000 to 60,000, are used in combination. The stabilizer (B1)
having a number average molecular weight of from 200 to 900 has a
weight average molecular weight of approximately from 200 to 900;
that is, the values of the number average molecular weight and the
weight average molecular weight of the stabilizer (B1) are roughly
the same.
[0241] In the case of using the stabilizer (B1) and the stabilizer
(B2) in combination, as the stabilizer, it is preferred that the
stabilizer (B1) is included in a larger amount, from the viewpoint
of improving the transparency.
[0242] Specifically, from the viewpoint of balancing the
transparency and the resistance to moist heat, the content of the
stabilizer (B2) is preferably within the range of from 10 parts by
mass to 150 parts by mass, and more preferably from 50 parts by
mass to 100 parts by mass, with respect to 100 parts by mass of the
stabilizer (B1).
[0243] Specific examples (stabilizers B-1 to B-3) of the stabilizer
(B) are shown below.
##STR00004##
[0244] The compound names, commercially available products, and the
like of the stabilizers B-1 to B-3 will be shown below. [0245]
Stabilizer B-1 The name of the compound is
bis-2,6-diisopropylphenyl carbodiimide. The stabilizer B-1 has a
weight average molecular weight (which means the same as "molecular
weight" in this case) of 363. Examples of commercially available
products thereof include "STABAXOL I" manufactured by Rhein Chemie
Rheinau GmbH, and "B2756" manufactured by Tokyo Chemical Industry
Co., Ltd. [0246] Stabilizer B-2 The name of the compound is
poly(4,4'-dicyclohexylmethanecarbodiimide). Examples of
commercially available products thereof which have a weight average
molecular weight of about 2,000 include "CARBODILITE LA-1"
manufactured by Nisshinbo Chemical Inc. [0247] Stabilizer B-3 The
name of the compound is
poly(1,3,5-triisopropylphenylene-2,4-carbodiimide). Examples of
commercially available products thereof which have a weight average
molecular weight of about 3,000 include "STABAXOL P" manufactured
by Rhein Chemie Rheinau GmbH. Further, examples thereof which have
a weight average molecular weight of 20,000 include "STABAXOL P400"
manufactured by Rhein Chemie Rheinau GmbH.
[0248] <Other Components>
[0249] The first piezoelectric body in the first embodiment may
include any of other components, if necessary.
[0250] Examples of other components include known resins such as
polyvinylidene fluorides, polyethylene resins, and polystyrene
resins; known inorganic fillers such as silica, hydroxyapatite, and
montmorillonite; known crystal nucleating agents such as
phthalocyanine; and stabilizers other than the stabilizer (B).
[0251] Examples of the inorganic filler and the crystal nucleating
agent include components disclosed in paragraphs 0057 to 0058 in WO
2013/054918.
[0252] (Degree of Orientation F)
[0253] The first piezoelectric body in the first embodiment has a
degree of orientation F of 0.5 or more but less than 1.0. However,
the degree of orientation F is preferably 0.7 or more but less than
1.0, and more preferably 0.8 or more but less than 1.0.
[0254] When the first piezoelectric body has a degree of
orientation F of 0.5 or more, molecular chains of the helical
chiral polymer (A) (such as molecular chains of polylactic acid)
which are aligned in the stretching direction are present in a
higher number. This leads to an increased ratio of oriented
crystals formed, thereby allowing the piezoelectric body to exhibit
an even higher piezoelectricity.
[0255] When the first piezoelectric body has a degree of
orientation F of less than 1.0, on the other hand, the
piezoelectric body will have a further improved longitudinal tear
strength.
[0256] (Degree of Crystallinity)
[0257] The degree of crystallinity of the first piezoelectric body
in the first embodiment is a value measured by the X-ray
diffraction (wide-angle x-ray diffraction measurement) described
above.
[0258] The first piezoelectric body in the first embodiment
preferably has a degree of crystallinity of from 20% to 80%, more
preferably from 25% to 70%, and still more preferably from 30% to
60%.
[0259] When the first piezoelectric body has a degree of
crystallinity of 20% or more, a high piezoelectricity can be
maintained. When the first piezoelectric body has a degree of
crystallinity of 80% or less, on the other hand, a high
transparency is maintained in the first piezoelectric body.
[0260] For example, in a case in which a piezoelectric film to be
used as a raw material of the first piezoelectric body is produced
by stretching, having a degree of crystallinity of 80% or less
makes the film less susceptible to whitening or rupture, thereby
facilitating the production of the first piezoelectric body.
Further, in a case in which a raw material (such as polylactic
acid) of the first piezoelectric body is produced by melt spinning,
followed by stretching, for example, having a degree of
crystallinity of 80% or less enables to produce a fiber having a
high bendability and flexible characteristics, thereby facilitating
the production of the first piezoelectric body.
[0261] (Transparency (Internal Haze))
[0262] The first piezoelectric body in the first embodiment is not
required to have transparency, in particular; however, the first
piezoelectric body may, of course, have transparency.
[0263] The transparency of the first piezoelectric body can be
evaluated by measuring an internal haze. The internal haze of the
first piezoelectric body as used herein refers to a haze from which
a haze caused by the shape of an outer surface of the first
piezoelectric body is excluded.
[0264] In a case in which the first piezoelectric body is required
to have transparency, the internal haze to visible light is
preferably 5% or less. From the viewpoint of further improving the
transparency and the longitudinal tear strength, the internal haze
is more preferably 2.0% or less, and still more preferably 1.0% or
less. The lower limit value of the internal haze of the first
piezoelectric body may be, for example, 0.01%, but not particularly
limited thereto.
[0265] The internal haze of the first piezoelectric body is a value
obtained by measuring the first piezoelectric body having a
thickness of from 0.03 mm to 0.05 mm, using a haze measuring
apparatus [TC-H III DPK, manufactured by Tokyo Denshoku Co., Ltd.]
in accordance with JIS-K7105, at 25.degree. C.
[0266] An example of the method of measuring the internal haze of
the first piezoelectric body will be shown below.
[0267] First, a sample 1 is prepared by sandwiching only a silicone
oil (SHINETSU SILICONE (trademark), model number: KF96-100CS,
manufactured by Shin-Etsu Chemical Co., Ltd.) between two glass
plates, and the haze (hereinafter, referred to as "haze (H2)") of
the sample 1 in the thickness direction is measured.
[0268] Next, a sample 2 is prepared by arranging a plurality of the
first piezoelectric bodies whose surfaces are uniformly wetted with
the silicone oil, without gaps, between two glass plates, and the
haze (hereinafter, referred to as "haze (H3)") of the sample 2 in
the thickness direction is measured.
[0269] Subsequently, the difference between these hazes is
calculated according to the following Equation, to obtain the
internal haze (H1) of the first piezoelectric body.
Internal haze (H1)=haze (H3)-haze (H2)
[0270] The measurements of the haze (H2) and the haze (H3) are each
carried out under the following measurement conditions, and using
the following apparatus.
[0271] Measuring apparatus: HAZE METER TC-H III DPK, manufactured
by Tokyo Denshoku Co., Ltd.
[0272] Sample size: 30 mm width.times.30 mm length
[0273] Measurement conditions: in accordance with JIS-K7105
[0274] Measurement temperature: room temperature (25.degree.
C.)
[0275] (Tensile Elastic Modulus)
[0276] The first piezoelectric body preferably has a tensile
elastic modulus of from 0.1 GPa to 100 GPa, and more preferably
from 1 GPa to 50 GPa.
[0277] In a case in which the first piezoelectric body is obtained
through a stretching step, the tensile elastic modulus refers to a
tensile elastic modulus in the stretching direction (MD
direction).
[0278] The first piezoelectric body may include polyvinylidene
fluoride, along with the helical chiral polymer (A) (such as a
polylactic acid polymer), from the viewpoint of further improving
the tensile elastic modulus.
[0279] In the case of this embodiment, the first piezoelectric body
preferably has a tensile elastic modulus of from 1 GPa to 10
GPa.
[0280] The method of measuring the tensile elastic modulus of the
first piezoelectric body is as follows.
[0281] In a case in which the first piezoelectric body is a film
(an example of an elongated flat plate form), a rectangular test
specimen (film) having a length of 100 mm is prepared. A value
obtained by dividing the mass (g) of the test specimen by the
density (g/cc) of the material thereof is taken as the volume of
the test specimen, and a value obtained by dividing the thus
obtained volume by the area (product of length and width) of the
main surface of the film is taken as an average thickness of the
test specimen. Based on the thus obtained thickness and the width
of the test specimen, a cross-sectional area of the test specimen
is calculated.
[0282] An S-S curve is plotted from the amount of stress and strain
when a tensile force is applied to the test specimen, using a
tensile tester (TENSILON RTG1250, manufactured by A&D Co.,
Ltd.), and the tensile elastic modulus is calculated from a slope
of initial linear strain region of the S-S curve.
[0283] In a case in which the first piezoelectric body is a thread
(an example of a fibrous form), a test specimen (thread) having a
length of 100 mm is prepared. A value obtained by dividing the mass
(g) of the test specimen by the density (g/cc) of the material
thereof is taken as the volume of the test specimen, and a value
obtained by dividing the thus obtained volume by the length of the
thread is taken as an average cross-sectional area of the test
specimen. An S-S curve is plotted from the amount of stress and
strain when a tensile force is applied to the test specimen, using
a tensile tester, and the tensile elastic modulus is calculated
from the slope of the initial linear strain region of the S-S
curve.
[0284] (Shape and Size of First Piezoelectric Body)
[0285] The piezoelectric substrate according to the first
embodiment includes the first piezoelectric body having an
elongated shape.
[0286] The first piezoelectric body having an elongated shape is
preferably a piezoelectric body in a fibrous form (in the form of a
thread) composed of a single bundle or a plurality of bundles, or a
piezoelectric body in the form of an elongated flat plate.
[0287] Descriptions will be given below in order, regarding the
piezoelectric body in a fibrous form (hereinafter, also referred to
as a "fibrous piezoelectric body"), and regarding the piezoelectric
body in the form of an elongated flat plate (hereinafter, also
referred to as an "elongated flat plate-like piezoelectric
body").
[0288] -Fibrous Piezoelectric Body--
[0289] The fibrous piezoelectric body may be, for example, a
monofilament thread or a multifilament thread.
[0290] Monofilament Thread
[0291] The monofilament thread preferably has a single fiber
fineness of from 3 dtex to 30 dtex, and more preferably from 5 dtex
to 20 dtex.
[0292] When the monofilament thread has a single fiber fineness of
less than 3 dtex, it becomes difficult to handle the thread in a
woven fabric preparation step or a weaving step. When the
monofilament thread has a single fiber fineness exceeding 30 dtex,
on the other hand, fusion bonding is more likely to occur between
the threads.
[0293] In view of the cost, it is preferable to directly obtain the
monofilament thread by spinning and stretching. The monofilament
thread may also be one obtained commercially or otherwise.
[0294] Multifilament Thread
[0295] The multifilament thread preferably has a total fineness of
from 30 dtex to 600 dtex, and more preferably from 100 dtex to 400
dtex.
[0296] As the multifilament thread, it is possible to use a
one-step thread such as a spin draw thread, or alternatively, a
two-step thread obtained by stretching a UDY (unstretched thread)
or a POY (highly-oriented unstretched thread). The multifilament
thread may also be one obtained commercially or otherwise.
[0297] Examples of commercially available products of polylactic
acid monofilament threads and polylactic acid multifilament threads
which can be used include: ECODEAR (registered trademark) PLA,
manufactured by Toray Industries, Inc.; TERRAMAC (registered
trademark), manufactured by Unitika Ltd.; and PLASTARCH (registered
trademark) manufactured by Kuraray Co., Ltd.
[0298] The method of producing the fibrous piezoelectric body is
not particularly limited, and the fibrous piezoelectric body can be
produced by a known method.
[0299] For example, a filament thread (such as a monofilament
thread or a multifilament thread) as the first piezoelectric body
can be obtained by melt spinning a raw material (such as polylactic
acid), followed by stretching the resultant (melt spinning drawing
method). After the spinning, it is preferred to maintain the
temperature of the atmosphere in the vicinity of the thread within
a constant range, until the thread is cooled and solidified.
[0300] Further, the filament thread as the first piezoelectric body
may be obtained, for example, by further separating the filament
thread obtained by the melt spinning drawing.
[0301] Cross-Sectional Shape
[0302] The fibrous piezoelectric body can be formed to have any of
various types of cross-sectional shapes, in a cross section taken
in the direction vertical to the longitudinal direction of the
fibrous piezoelectric body, such as for example, a cross-sectional
shape in the form of a circle, an oval, a rectangle, a cocoon, a
ribbon, a quatrefoil, a star, or a deformed shape.
[0303] -Elongated Flat Plate-Like Piezoelectric Body--
[0304] The elongated flat plate-like piezoelectric body may be, for
example, an elongated flat plate-like piezoelectric body (such as a
slit ribbon) obtained by slitting a piezoelectric film produced by
a known method or a piezoelectric film obtained commercially or
otherwise.
[0305] In a case in which the piezoelectric substrate according to
the first embodiment includes the first piezoelectric body is in
the form of an elongated flat plate, a functional layer may be
provided on at least one of the main surfaces of the first
piezoelectric body, to the extent that the effect of the first
embodiment is not impaired.
[0306] The functional layer may have a monolayer structure, or a
structure composed of two or more layers.
[0307] For example, in a case in which the functional layer is
provided on both main surfaces of the elongated flat plate-like
piezoelectric body, each of the functional layer provided on one of
the main surfaces (hereinafter, referred to as a "top surface" for
convenience) and the functional layer provided on the other main
surface (hereinafter, referred to as a "back surface" for
convenience) may independently have a monolayer structure or a
structure composed of two or more layers.
[0308] The functional layer may be, for example, any of various
kinds of functional layers.
[0309] Examples of the functional layer include an easily-adhesive
layer, a hard coat layer, a refractive index controlling layer, an
anti-reflection layer, an anti-glare layer, a slippery layer, an
anti-blocking layer, a protective layer, an adhesive layer, an
antistatic layer, a heat dissipation layer, a UV-absorbing layer,
an Anti-Newton ring layer, a light scattering layer, a polarization
layer, a gas barrier layer, and a hue adjustment layer.
[0310] The functional layer may be a layer composed of two or more
of these layers.
[0311] The functional layer may also be a layer having two or more
functions of these layers.
[0312] In a case in which the functional layer is provided on both
main surfaces of the elongated flat plate-like piezoelectric body,
the functional layer provided on the side of the top surface may be
the same as, or different from the functional layer provided on the
side of the back surface.
[0313] Further, the effects provided by the functional layer
include an effect of fixing defects, for example, an effect of
filling die lines and dents, on the surface of the elongated flat
plate-like piezoelectric body, thereby improving the appearance. In
this case, a lower difference in refractive index between the
elongated flat plate-like piezoelectric body and the functional
layer results in a lower reflection at the interface of the
elongated flat plate-like piezoelectric body and the functional
layer, thereby further improving the appearance.
[0314] The functional layer preferably includes at least one of the
easily-adhesive layer, the hard coat layer, the antistatic layer,
the anti-blocking layer, or the protective layer. This facilitates
the application of the piezoelectric substrate to a piezoelectric
device (such as a piezoelectric woven fabric or a piezoelectric
knitted fabric), a force sensor, an actuator, or a device for
obtaining biological information.
[0315] In a case in which the piezoelectric substrate according to
the first embodiment includes the first piezoelectric body in the
form of an elongated flat plate, an electrode layer may be provided
on at least one (preferably both) of the main surfaces of the first
piezoelectric body.
[0316] The electrode layer may be provided in contact with the
elongated flat plate-like piezoelectric body, or provided with the
functional layer interposed therebetween.
[0317] In a case in which the piezoelectric substrate according to
the first embodiment which includes the elongated flat plate-like
piezoelectric body in the above described arrangement, is used as
one of the components of, for example, a piezoelectric device (such
as a piezoelectric woven fabric or a piezoelectric knitted fabric),
a force sensor, an actuator, or a device for obtaining biological
information, it is possible, for example, to more easily connect an
extraction electrode for extracting the electric charge generated
in the piezoelectric substrate, with a laminated body. As a result,
the productivity of the resulting piezoelectric device (such as the
piezoelectric woven fabric or the piezoelectric knitted fabric),
the force sensor, the actuator, or the device for obtaining
biological information will be improved.
[0318] Materials for the functional layer are not particularly
limited, and examples thereof include: inorganic substances such as
metals and metal oxides; organic substances such as resins; and
composite compositions containing a resin(s) and fine particles. As
the resin, it is possible to use, for example, a cured product
obtained by curing a resin, by controlling the temperature or using
an active energy ray. In other words, a curable resin can be used
as the resin.
[0319] Examples of the curable resin include at least one material
(curable resin) selected from the group consisting of: acrylic
compounds, methacrylic compounds, vinyl compounds, allyl compounds,
urethane compounds, epoxy compounds, epoxide compounds, glycidyl
compounds, oxetane compounds, melamine compounds, cellulose
compounds, ester compounds, silane compounds, silicone compounds,
siloxane compounds, silica-acrylic hybrid compounds, and
silica-epoxy hybrid compounds.
[0320] Among these, an acrylic compound, an epoxy compound, or a
silane compound is more preferred.
[0321] The metal may be, for example, at least one selected from
Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, In, Sn, W, Ag, Au, Pd, Pt,
Sb, Ta or Zr; or an alloy thereof.
[0322] The metal oxide may be, for example, at least one of
titanium oxide, zirconium oxide, zinc oxide, niobium oxide,
antimony oxide, tin oxide, indium oxide, cerium oxide, aluminum
oxide, silicon oxide, magnesium oxide, yttrium oxide, ytterbium
oxide, or tantalum oxide; or a composite oxide thereof.
[0323] Examples of the fine particles include fine particles of
metal oxides as described above; and fine particles of resins such
as fluororesins, silicone resins, styrene resins, and acrylic
resins. Examples also include hollow fine particles which are the
above described fine particles having internal cavities.
[0324] The fine particles preferably have an average primary
particle size of from 1 nm to 500 nm, more preferably from 5 nm to
300 nm, and still more preferably from 10 nm to 200 nm, from the
viewpoint of improving the transparency. Having an average primary
particle size of 500 nm or less prevents the scattering of a
visible light, whereas having an average primary particle size of 1
nm or more prevents secondary aggregation of fine particles;
therefore, an average primary particle size within this range is
desirable from the viewpoint of maintaining the transparency.
[0325] The functional layer preferably has a film thickness within
the range of from 0.01 .mu.m to 10 .mu.m, but not particularly
limited thereto.
[0326] The upper limit value of the thickness is more preferably 6
.mu.m or less, and still more preferably 3 .mu.m or less. Further,
the lower limit value thereof is more preferably 0.01 .mu.m or
more, and sill more preferably 0.02 .mu.m or more.
[0327] In a case in which the functional layer is a multilayer film
composed of a plurality of functional layers, the thickness of the
functional layer refers to the thickness of the entire multilayer
film. Further, the functional layer may be provided on both
surfaces of the elongated flat plate-like piezoelectric body. In
addition, the functional layers may have a refractive index
different from each other.
[0328] The method of producing the elongated flat plate-like
piezoelectric body is not particularly limited, and the elongated
flat plate-like piezoelectric body can be produced by a known
method.
[0329] For example, the first piezoelectric body can be produced
from a piezoelectric film, by a method in which a raw material
(such as polylactic acid) is formed in the form of a film to obtain
an unstretched film, and the resulting unstretched film is
subjected to stretching and crystallization, followed by slitting
the resulting piezoelectric film.
[0330] The term "slitting" as used herein refers to cutting the
piezoelectric film into an elongated shape.
[0331] Either the stretching or the crystallization may be carried
out first. Further, a method may also be used in which an
unstretched film is subjected to pre-crystallization, stretching,
and crystallization (annealing) are carried out in this order. The
stretching of the film may be carried out by uniaxial stretching or
biaxial stretching. In the case of stretching the film by biaxial
stretching, the draw ratio in one direction (the main stretching
direction) is preferably adjusted to a higher magnification.
[0332] As to the method of producing a piezoelectric film, methods
disclosed in known literature, such as JP-B No. 4934235, WO
2010/104196, WO 2013/054918, and WO 2013/089148, can be referred
to, as appropriate.
[0333] <Fiber>
[0334] The piezoelectric substrate according to the first
embodiment may include a fiber.
[0335] It is preferred that the fiber is wound in a direction
different from the one direction (the winding direction of the
first piezoelectric body), and that the first piezoelectric body
and the fiber are alternately crossed with each other to be formed
into a braided structure.
[0336] The winding direction (right-handed or left-handed
direction) of the fiber may be the same as, or different from the
winding direction of the first piezoelectric body.
[0337] The fiber is not particularly limited, and examples thereof
include: polymer fibers such as aramid fibers, polyester fibers,
acrylic fibers, polyethylene fibers, polypropylene fibers, vinyl
chloride fibers, polysulfone fibers, polyether fibers, and
polyurethane fibers; natural fibers such as cotton, hemp, silk, and
cellulose; semi-synthetic fibers such as acetate; regenerated
fibers such as rayon and cupra; and glass fibers. Further, the
fiber may also be, for example, the second piezoelectric body in
the form of a fiber.
[0338] These fibers may be used singly, or in combination of two or
more kinds thereof.
[0339] The fiber may be, for example, a monofilament thread or a
multifilament thread. The monofilament thread may have, for
example, a single fiber fineness within the same range as the
single fiber fineness of the monofilament thread in the previously
described fibrous piezoelectric body. The multifilament thread may
have, for example, a total fineness within the same range as the
total fineness of the multifilament thread in the previously
described fibrous piezoelectric body.
[0340] <Second Piezoelectric Body>
[0341] The piezoelectric substrate according to the first
embodiment may include a second piezoelectric body having an
elongated shape.
[0342] It is preferred that the second piezoelectric body is wound
in a direction different from the one direction (the winding
direction of the first piezoelectric body), and that the first
piezoelectric body and the second piezoelectric body are
alternately crossed with each other to be formed into a braided
structure.
[0343] The second piezoelectric body preferably has the same
properties as the properties of the first piezoelectric body.
[0344] In other words, it is preferred that:
[0345] the second piezoelectric body includes a helical chiral
polymer (A) having an optical activity;
[0346] the length direction of the second piezoelectric body is
substantially parallel to the main direction of orientation of the
helical chiral polymer (A) included in the second piezoelectric
body; and
[0347] the second piezoelectric body has a degree of orientation F,
as measured by X-ray diffraction according to the Equation (a),
within the range of 0.5 or more but less than 1.0.
[0348] The second piezoelectric body preferably has other
properties which are the same as the first piezoelectric body, in
addition to the properties described above.
[0349] In a case in which the first piezoelectric body and the
second piezoelectric body are alternately crossed with each other
to be formed into a braided structure, it is preferred that the
helical chiral polymer (A) included in the first piezoelectric body
has a chirality different from the chirality of the helical chiral
polymer (A) included in the second piezoelectric body.
[0350] Further, the second piezoelectric body may have properties
different from the properties of the first piezoelectric body.
[0351] The second piezoelectric body may include the stabilizer (B)
and any of other components, in the same manner as the previously
described first piezoelectric body.
[0352] <Adhesive Composition>
[0353] The first piezoelectric body in the first embodiment
preferably includes an adhesive composition, from the viewpoint of
improving the piezoelectric sensitivity, and the piezoelectric
output stability.
[0354] The term "adhesion" is used as a concept encompassing the
concept of "pressure-sensitive adhesion". Further, the term
"adhesive" is used as a concept encompassing the concept of
"pressure-sensitive adhesive".
[0355] The adhesive composition is sometimes referred to as the
"adhesive", in the description given below.
[0356] The adhesive is used in order to mechanically integrate the
portions of the first piezoelectric body.
[0357] In a case in which the first piezoelectric body includes the
adhesive, the relative positions of the portions of the first
piezoelectric body are less likely to be displaced when a tensile
force is applied to the piezoelectric substrate according to the
first embodiment, making the tensile force to be more efficiently
applied to the first piezoelectric body. This allows for an
effective detection of a voltage output proportional to the tensile
force. As a result, the piezoelectric sensitivity, and the
piezoelectric output stability are further improved. Further, when
the first piezoelectric body includes the adhesive, the absolute
value of the amount of electric charge generated (surface potential
generated) per unit tensile force, in the piezoelectric substrate,
will be further increased.
[0358] In contrast, in a piezoelectric substrate in which the first
piezoelectric body does not include the adhesive, flexible
properties will be maintained even after being processed into a
piezoelectric fiber (such as a piezoelectric knitted fabric, or a
piezoelectric woven fabric) to be described later, enabling to
provide a favorable feeling of fit when used in a wearable sensor
or the like.
[0359] Materials shown below can be used as the materials for the
adhesive composition (adhesive).
[0360] Examples of materials which can be used include: epoxy
adhesives, urethane adhesives, vinyl acetate resin emulsion
adhesives, (EVA) emulsion adhesives, acrylic resin emulsion
adhesives, styrene-butadiene rubber latex adhesives, silicone resin
adhesives, a-olefin (isobutene-maleic anhydride resin) adhesives,
vinyl chloride resin solvent adhesives, rubber adhesives, elastic
adhesives, chloroprene rubber solvent adhesives, nitrile rubber
solvent adhesives, and cyanoacrylate adhesives.
[0361] -Thickness--
[0362] The thickness of portions bonded with the adhesive in the
first embodiment is "the thinner the better", as long as no gap is
formed between the objects or portions to be bonded, and the
strength of the bonding is not decreased. When the thickness of the
bonded portions is decreased, the strain generated by the tensile
force applied to the piezoelectric substrate becomes less likely to
be alleviated at the portions of the adhesive, thereby efficiently
decreasing the strain in the first piezoelectric body. As a result,
in a case in which the piezoelectric substrate according to the
first embodiment is used, for example, in a sensor, the sensitivity
of the resulting sensor will be improved.
[0363] -Method of Coating Adhesive--
[0364] The method of coating the adhesive is not particularly
limited, and it is possible to use, mainly, the following two
methods.
[0365] Method in which Adhesive is Disposed After Processing,
Followed by Bonding
[0366] Examples of this method include a method in which: the first
piezoelectric body is disposed; in a case in which the
piezoelectric substrate includes a fiber, the fiber and the first
piezoelectric body are disposed; in a case in which the
piezoelectric substrate includes an electrode, the electrode is
processed and disposed; and after completing the disposition of
respective members to be included in the substrate, in addition to
the above dispositions, the adhesive is disposed between the
portions of the respective members (for example, between the
portions of the first piezoelectric body), and at the interfaces
between the respective members and the like, by a technique such as
coating, e.g. dip coating, or impregnation, so that the respective
portions and members are adhered with each other.
[0367] Method in which Uncured Adhesive is Disposed before
Processing, and Bonded after Processing
[0368] Examples of this method include a method in which: a
photocurable adhesive, a thermosetting adhesive, a thermoplastic
adhesive, or the like is coated on a surface of the first
piezoelectric body using a gravure coater, a dip coater, or the
like, in advance, followed by drying, and then, for example, the
first piezoelectric body is disposed; in a case in which the
piezoelectric substrate includes a fiber, the fiber and the first
piezoelectric body are disposed; in a case in which the
piezoelectric substrate includes an electrode, the electrode is
processed and disposed; and after completing the disposition of
respective members to be included in the substrate, in addition to
the above dispositions, the adhesive is cured by UV irradiation or
heating, so that the portions of the respective members and the
interfaces between the respective members, and the like are bonded
with each other.
[0369] Further, in a case in which the piezoelectric substrate
according to the first embodiment is processed into a piezoelectric
knitted fabric or a piezoelectric woven fabric to be described
later, the portions of the respective members (such as the portions
of the first piezoelectric body), the interfaces between the
respective members, and the like, for example, may be bonded or
heat fused with each other, in the same manner as described above,
after being processed into the piezoelectric knitted fabric or the
piezoelectric woven fabric. In this case, the piezoelectric knitted
fabric or the piezoelectric woven fabric can be processed easily,
since the knitted fabric or the woven fabric maintains flexible
properties before the respective members or the portions thereof
are integrated by the adhesive.
[0370] The above method is characterized in that: it allows for
processing by a dry process, after the adhesive has been coated and
dried, thereby facilitating the processing; and that it enables to
easily form a coating film having a uniform thickness, thereby
reducing a variation in sensor sensitivity etc.
[0371] <Method of Producing Piezoelectric Substrate>
[0372] The method of producing the piezoelectric substrate
according to the first embodiment is not particularly limited, and
the piezoelectric substrate can be produced, for example, by
preparing the first piezoelectric body, and helically winding the
first piezoelectric body in one direction with respect to the
helical axis.
[0373] Further, the piezoelectric substrate according to the first
embodiment can also be prepared, for example, by using a fiber
which is soluble by a specific action (such as a thread soluble in
water), and helically winding the first piezoelectric body around
the fiber in one direction, followed by allowing the fiber to
dissolve over time, or dissolving and removing the fiber with
water, as described above. Further, the piezoelectric substrate can
also be produced by helically winding the first piezoelectric body
around a core material in one direction, followed by removing the
core material.
[0374] The first piezoelectric body may be one produced by a known
method, or one obtained commercially or otherwise.
[0375] In a case in which the piezoelectric substrate according to
the first embodiment includes a fiber, and the first piezoelectric
body and the fiber are formed into a braided structure, the
piezoelectric substrate can be produced by alternately crossing and
winding the first piezoelectric body and the fiber, in accordance
with the method of winding the first piezoelectric body.
[0376] Further, in a case in which the piezoelectric substrate
according to the first embodiment includes a second piezoelectric
body, and the first piezoelectric body and the second piezoelectric
body are formed into a braided structure, the piezoelectric
substrate can be produced by alternately crossing and winding the
first piezoelectric body and the second piezoelectric body in the
same manner, in accordance with the method of winding the first
piezoelectric body.
[0377] Still further, in a case in which the piezoelectric
substrate according to the first embodiment includes an electrode,
the piezoelectric substrate can be produced by disposing the
electrode by a known method.
[0378] It is to be noted that, preferably, the adhesive is used to
bind between the portions of the first piezoelectric body, and if
necessary, between the fiber and the first piezoelectric body,
between the first piezoelectric body and the second piezoelectric
body, and between the respective members included in the
piezoelectric substrate according to the first embodiment, for
example, by any of the previously described methods.
[0379] The second embodiment of the piezoelectric substrate
according to the present disclosure will now be described in
detail.
[0380] [Piezoelectric Substrate according to Second Embodiment]
[0381] The piezoelectric substrate according to the second
embodiment includes:
[0382] a core material having an elongated shape; and
[0383] a first piezoelectric body having an elongated shape and
helically wound in one direction with respect to the core
material,
[0384] wherein the core material is a non-electrically conductive
core material,
[0385] wherein the first piezoelectric body includes a helical
chiral polymer (A) having an optical activity,
[0386] wherein the length direction of the first piezoelectric body
is substantially parallel to the main direction of orientation of
the helical chiral polymer (A) included in the first piezoelectric
body, and
[0387] wherein the first piezoelectric body has a degree of
orientation F, as measured by X-ray diffraction according to the
following Equation (a), within the range of 0.5 or more but less
than 1.0.
Degree of orientation F=(180.degree.-.alpha.)/180.degree. (a)
In the Equation (a), .alpha. represents the half-value width of the
peak derived from the orientation. The unit of .alpha. is ".degree.
(degree(s))".
[0388] The piezoelectric substrate according to the second
embodiment differs from the piezoelectric substrate according to
the first embodiment, in that it includes a core material which is
not electrically conductive (non-electrically conductive core
material), and that the first piezoelectric body is helically wound
around the non-electrically conductive core material in one
direction.
[0389] Being "non-electrically conductive" refers to having a
volume resistivity of 10.sup.8 .OMEGA.cm or more.
[0390] The expression "the first piezoelectric body helically wound
in one direction with respect to the core material" means that the
first piezoelectric body is helically wound in one direction, along
an outer peripheral surface of the core material.
[0391] The definitions of the "degree of orientation F" and the
"one direction" are the same as described above.
[0392] By having the above configuration, the piezoelectric
substrate according to the second embodiment has an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0393] The piezoelectric substrate according to the second
embodiment has piezoelectricity, due to the same reason as
described for the piezoelectric substrate according to the first
embodiment.
[0394] Further, in the piezoelectric substrate according to the
second embodiment, the disposition of the first piezoelectric body
in the above described arrangement allows a shear force to be
applied to the helical chiral polymer (A), when a tensile force
(stress) is applied in the length direction of the piezoelectric
substrate. As a result, the polarization of the helical chiral
polymer (A) occurs in the radial direction of the piezoelectric
substrate. In a case in which the helically wound, first
piezoelectric body is regarded as an aggregate of micro-regions
which can be roughly considered as a plain in the length direction
of the piezoelectric body, and when the shear force generated due
to the tensile force (stress) in the plain composed of the
micro-regions is applied to the helical chiral polymer, the
direction of the polarization roughly matches the direction of the
electric field generated due to the piezoelectric stress constant
d.sub.14.
[0395] Specifically, in the case of polylactic acid, such as, for
example, in the case of a homopolymer of an L-lactic acid (PLLA)
having a molecular structure in the form of a left-handed helix,
when the first piezoelectric body in which the main direction of
orientation of PLLA is substantially parallel to the length
direction of the piezoelectric body is helically wound in the
left-handed direction with respect to a non-electrically conductive
core material to obtain a structure, and when a tensile force
(stress) is applied to the structure, an outward electric field
(polarization) is generated in the direction parallel to the radial
direction, from the center of the circle of the circular cross
section vertical to the tensile force. Conversely, when the first
piezoelectric body in which the main direction of orientation of
PLLA is substantially parallel to the length direction of the
piezoelectric body is helically wound in the right-handed direction
with respect to a non-electrically conductive core material to
obtain a structure, and when a tensile force (stress) is applied to
the structure, an inward electric field (polarization) is generated
in the direction parallel to the radial direction, from the outer
periphery of the circle of the circular cross section vertical to
the tensile force.
[0396] Further, for example, in the case of homopolymer of a
D-lactic acid (PDLA) having a molecular structure in the form of a
right-handed helix, when the first piezoelectric body in which the
main direction of orientation of PDLA is substantially parallel to
the length direction of the piezoelectric body is helically wound
in the left-handed direction with respect to a non-electrically
conductive core material to obtain a structure, and when a tensile
force (stress) is applied to the structure, an inward electric
field (polarization) is generated in the direction parallel to the
radial direction, from the outer periphery of the circle of the
circular cross section vertical to the tensile force. Conversely,
when the first piezoelectric body in which the main direction of
orientation of PDLA is substantially parallel to the length
direction of the piezoelectric body is helically wound in the
right-handed direction with respect to a non-electrically
conductive core material to obtain a structure, and when a tensile
force (stress) is applied to the structure, an outward electric
field (polarization) is generated in the direction parallel to the
radial direction, from the center of the circle of the circular
cross section vertical to the tensile force.
[0397] As a result, when a tensile force is applied in the length
direction of the piezoelectric substrate, a potential difference
proportional to the tensile force is generated at respective
portions of the helically disposed first piezoelectric body, in a
phase matched manner, and this is thought to allow for an effective
detection of a voltage signal proportional to the tensile
force.
[0398] Therefore, the piezoelectric substrate according to the
second embodiment has an excellent piezoelectric sensitivity as
well as excellent piezoelectric output stability.
[0399] Further, the piezoelectric substrate according to the second
embodiment includes a non-electrically conductive core material as
a core material, and has a structure in which the first
piezoelectric body is helically wound around the non-electrically
conductive core material in one direction.
[0400] Here, a piezoelectric substrate including an electrically
conductive core material as the core material can also be
considered. However, in such a piezoelectric substrate, the metal
conductor portion of the electrically conductive core material
tends to be susceptible to breakage due to fatigue, as a result of
the application of a load, such as repeated bending.
[0401] Accordingly, the piezoelectric substrate according to the
second embodiment has an improved resistance to a load such as
repeated bending or to deformation, as compared to the
piezoelectric substrate including the electrically conductive core
material.
[0402] The embodiment in which the first piezoelectric body is
helically wound in one direction with respect to the
non-electrically conductive core material is not particularly
limited. Examples thereof include: an embodiment in which the first
piezoelectric body is helically wound in one direction at a
predetermined helix angle, from one end to the other, along the
outer peripheral surface of the non-electrically conductive core
material; and an embodiment in which the non-electrically
conductive core material and the first piezoelectric body are
twisted with each other around the same pivot axis.
[0403] Specific embodiments of the piezoelectric substrate
according to the second embodiment will now be described.
[0404] Specific Embodiment C of the piezoelectric substrate
according to the second embodiment will be described below, with
reference to the drawings. In the description given below, the
repetition of the description given in Specific Embodiment A will
be omitted.
[0405] In the piezoelectric substrate of Specific Embodiment C, the
first piezoelectric body is helically wound in one direction with
respect to a non-electrically conductive core material at a
predetermined helix angle, from one end to the other.
[0406] [Specific Embodiment C]
[0407] FIG. 3 is a side view showing Specific Embodiment C of the
piezoelectric substrate according to the second embodiment.
[0408] A piezoelectric substrate 10B of Specific Embodiment C
differs from the piezoelectric substrate 10 of Specific Embodiment
A in the first embodiment, in that the piezoelectric substrate 10B
includes a non-electrically conductive core material 12A in the
interior of the piezoelectric substrate.
[0409] In other words, the piezoelectric substrate 10B of Specific
Embodiment C includes the non-electrically conductive core material
12A, and the first piezoelectric body 14A having an elongated
shape.
[0410] The first piezoelectric body 14A is helically wound in one
direction with respect to the non-electrically conductive core
material 12A at the helix angle .beta.1, from one end to the other,
such that no gap is formed.
[0411] The "helix angle .beta.1" refers to the angle formed between
the axial direction of the non-electrically conductive core
material 12A, namely, a helical axis G3, and the arrangement
direction of the first piezoelectric body 14A with respect to the
helical axis G3.
[0412] The piezoelectric substrate 10B of Specific Embodiment C
allows for an effective detection of a voltage signal proportional
to the applied tensile force, due to the same reason as described
in Specific Embodiment A.
[0413] Further, in the piezoelectric substrate 10B, since the first
piezoelectric body 14A is impregnated with an adhesive (not shown
in the figure), in the same manner as in the piezoelectric
substrate 10 of Specific Embodiment A, the relative positions of
the portions of the first piezoelectric body 14A are less likely to
be displaced, allowing a tensile force to be more effectively
applied to the first piezoelectric body 14A.
[0414] In addition, since the piezoelectric substrate 10B includes
the non-electrically conductive core material 12A as a core
material, breakage due to fatigue is reduced as compared to the
case of including an electrically conductive core material (such as
a core material made of metal).
[0415] The above described arrangements allow the piezoelectric
substrate 10B of Specific Embodiment C to have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0416] Next, Specific Embodiments D1 and D2 of the piezoelectric
substrates according to the second embodiment will be described
with reference to the drawings. In the description given below, the
repetition of the descriptions given in Specific Embodiments B1 and
B2 will be omitted.
[0417] In each of the piezoelectric substrates of Specific
Embodiments D1 and D2, the first piezoelectric body is helically
wound in one direction with respect to a non-electrically
conductive core material at a predetermined helix angle, from one
end to the other.
[0418] [Specific Embodiment D1]
[0419] FIG. 4 is a side view showing Specific Embodiment D1 of the
piezoelectric substrate according to the first embodiment.
[0420] A piezoelectric substrate 10C of Specific Embodiment D1
differs from the piezoelectric substrate 10A of Specific Embodiment
B1 in the first embodiment, in that the piezoelectric substrate 10C
includes the non-electrically conductive core material 12A in the
interior of the piezoelectric substrate.
[0421] In other words, in the piezoelectric substrate 10C of
Specific Embodiment D1, the first piezoelectric body 14A and the
second piezoelectric body 14B are alternately crossed with each
other to be formed into a braided structure.
[0422] The piezoelectric substrate 10C of Specific Embodiment D1
allows for an effective detection of a voltage signal proportional
to the applied tensile force, due to the same reason as described
in Specific Embodiment B1.
[0423] Further, since the piezoelectric substrate 10C includes the
non-electrically conductive core material 12A as a core material,
breakage due to fatigue is reduced as compared to the case of
including an electrically conductive core material (such as a core
material made of metal).
[0424] The above described arrangements allow the piezoelectric
substrate 10C of Specific Embodiment D1 to have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0425] Further, the piezoelectric substrate 10C of Specific
Embodiment D1 can be suitably used as a constituent member in a
product which needs to conform to a three-dimensional plane, for
example, a wearable product (such as a piezoelectric woven fabric,
a piezoelectric knitted fabric, a force sensor, or a device for
obtaining biological information, to be described later), due to
the same reason as described in Specific Embodiment B1.
[0426] Next, Specific Embodiment D2 of the piezoelectric substrate
according to the second embodiment will be described with reference
to the drawings. In the description given below, the repetition of
the descriptions given in Specific Embodiments B1 and B2 will be
omitted.
[0427] [Specific Embodiment D2]
[0428] The piezoelectric substrate of Specific Embodiment D2 has
the same configuration as the piezoelectric substrate 10C of
Specific Embodiment D1, except for including a fiber instead of the
second piezoelectric body 14B, in the piezoelectric substrate 10C
of Specific Embodiment D1 shown in FIG. 4. In other words, the
piezoelectric substrate of Specific Embodiment D2 is a
piezoelectric substrate in which the first piezoelectric body and
the fiber are alternately crossed with each other to be formed into
a braided structure. Further, the fiber in Specific Embodiment D2
is a fiber which does not have piezoelectricity. In the case of
this embodiment, the winding direction of the fiber may be
right-handed or left-handed.
[0429] In Specific Embodiment D2, when the piezoelectric substrate
is bent and deformed, the state in which the first piezoelectric
body is wound in one direction with respect to the non-electrically
conductive core material is more easily retained, in the same
manner as in Specific Embodiment B2. This facilitates the
occurrence of polarization in the helical chiral polymer (A)
included in the first piezoelectric body, when a tensile force is
applied in the length direction of the piezoelectric substrate.
[0430] Further, since the piezoelectric substrate of Specific
Embodiment D2 includes the non-electrically conductive core
material as a core material, breakage due to fatigue is reduced as
compared to the piezoelectric substrate including an electrically
conductive core material (such as a core material made of
metal).
[0431] The above described arrangements allow the piezoelectric
substrate of Specific Embodiment D2 to also have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation
[0432] Next, Specific Embodiment E of the piezoelectric substrate
according to the second embodiment will be described with reference
to the drawings.
[0433] Specific Embodiment E is an embodiment in which a
non-electrically conductive core material and the first
piezoelectric body are twisted with each other around the same
pivot axis.
[0434] [Specific Embodiment E]
[0435] FIG. 5 is a side view showing Specific Embodiment E of the
piezoelectric substrate according to the second embodiment.
[0436] As shown in FIG. 5, in a piezoelectric substrate 10D
according to the second embodiment, a non-electrically conductive
core material 12B having an elongated shape and a first
piezoelectric body 14C having an elongated shape are twisted with
each other around the same pivot axis G5, at the same number of
twists. More specifically, in the piezoelectric substrate 10D of
Specific Embodiment E, the first piezoelectric body 14C is
helically wound in the right-handed direction with respect to the
pivot axis G5.
[0437] The expression "wound in the right-handed direction" as used
herein means that, when the piezoelectric substrate 10D is seen
from one end side of the direction of the pivot axis G5 (on the
right side, in the case of FIG. 5), the first piezoelectric body
14C is wound in the right-handed direction, from the near side to
the far side of the pivot axis G5.
[0438] In FIG. 5, the non-electrically conductive core material 12B
and the first piezoelectric body 14C are twisted at a number of
twists of "3". In this case, in FIG. 5, the number of twists per
length L1 of the piezoelectric substrate 10D is "3", and the
distance between the portions of the first piezoelectric body 14C
per one winding is L2 (the same applies for the distance between
the portions of the non-electrically conductive core material 12B).
Further, in FIG. 5, the angle formed between the pivot axis G5 and
the length direction of the first piezoelectric body 14C is
.beta.3.
[0439] Further, in FIG. 5, the main direction of orientation of the
helical chiral polymer (A) included in the first piezoelectric body
14C is indicated by a two-way arrow E3. In other words, the main
direction of orientation of the helical chiral polymer (A) is
substantially parallel to the arrangement direction of the first
piezoelectric body 14C.
[0440] The functions of the piezoelectric substrate 10D according
to the second embodiment will be described below.
[0441] For example, when a tensile force is applied to the length
direction of the piezoelectric substrate 10D, a shear force is
applied to the helical chiral polymer (A) included in the first
piezoelectric body 14C, and polarization occurs in the helical
chiral polymer (A) included in the first piezoelectric body 14C.
The polarization of the helical chiral polymer (A) occurs in the
radial direction of the piezoelectric substrate 10D, and it is
thought that the polarization occurs in that direction in a phase
matched manner. This allows for an effective detection of a voltage
signal proportional to the tensile force.
[0442] In the piezoelectric substrate 10D, in particular, the
non-electrically conductive core material 12B and the first
piezoelectric body 14C are merely twisted with each other.
Therefore, the cross-sectional areas of the non-electrically
conductive core material 12B and the first piezoelectric body 14C
can be reduced, as a result of which a thinner piezoelectric
substrate 10D can be obtained. Accordingly, a high bendability and
flexibility (ductility) can be easily imparted to the piezoelectric
substrate, making the resulting piezoelectric substrate
particularly suitable for being processed into a piezoelectric
woven fabric, a piezoelectric knitted fabric, or the like to be
described later.
[0443] Further, since the piezoelectric substrate 10D includes the
non-electrically conductive core material 12B as a core material,
breakage due to fatigue is reduced as compared to the case of
including an electrically conductive core material (such as a core
material made of metal).
[0444] The above described arrangements allow the piezoelectric
substrate 10D of Specific Embodiment E to have an excellent
piezoelectric sensitivity, an excellent piezoelectric output
stability, and an improved resistance to a load such as repeated
bending or to deformation.
[0445] Materials and the like included in the piezoelectric
substrate according to the second embodiment will be now
described.
[0446] The piezoelectric substrate according to the second
embodiment is in no way limited by the configuration of the
piezoelectric substrate according to the first embodiment.
[0447] <Non-Electrically Conductive Core Material>
[0448] The piezoelectric substrate according to the second
embodiment includes a non-electrically conductive core material
having an elongated shape, as a core material.
[0449] Materials for the non-electrically conductive core material
are not particularly limited, as long as the materials do not have
electrical conductivity. Examples thereof include: polymer resins
such as polyamide resins, polyester resins, acrylic resins,
polyethylene resins, polypropylene resins, polyvinyl chloride
resins, polysulfone resins, polyether resins, and polyurethane
resins; cellulose resins; and inorganic materials such as glass,
silica gel, and ceramics. These materials may be used singly, or in
combination of two or more kinds thereof.
[0450] The shape (elongated shape) and the major axis diameter of
the non-electrically conductive core material are not particularly
limited. However, the non-electrically conductive core material is
preferably a core material in a fibrous form composed of a single
bundle or a plurality of bundles.
[0451] The core material in a fibrous form may be, for example, a
thread (a monofilament thread or a multifilament thread).
[0452] <First Piezoelectric Body>
[0453] The definition and preferred embodiments of the first
piezoelectric body in the second embodiment are the same as the
definition and preferred embodiments of the first piezoelectric
body in the first embodiment.
[0454] Further, the definition and preferred embodiments of the
helical chiral polymer (A) included in the first piezoelectric body
in the second embodiment are the same as the definition and
preferred embodiments of the helical chiral polymer (A) included in
the first piezoelectric body in the first embodiment.
[0455] <Fiber>
[0456] The piezoelectric substrate according to the second
embodiment may include a fiber.
[0457] The fiber is preferably wound in a direction different from
the one direction (the winding direction of the first piezoelectric
body). In addition, it is preferred that the first piezoelectric
body and the fiber are alternately crossed with each other to be
formed into a braided structure.
[0458] The definition and preferred embodiments of the fiber in the
second embodiment are the same as the definition and preferred
embodiments of the fiber in the first embodiment.
[0459] <Second Piezoelectric Body>
[0460] The piezoelectric substrate according to the second
embodiment may include a second piezoelectric body having an
elongated shape.
[0461] The second piezoelectric body is preferably wound in a
direction different from the one direction (the winding direction
of the first piezoelectric body). In addition, it is preferred that
the first piezoelectric body and the second piezoelectric body are
alternately crossed with each other to be formed into a braided
structure.
[0462] The definition and preferred embodiments of the second
piezoelectric body in the second embodiment are the same as the
definition and preferred embodiments of the second piezoelectric
body in the first embodiment.
[0463] The second piezoelectric body in the second embodiment may
include the stabilizer (B) and any of other components, in the same
manner as the second piezoelectric body in the first
embodiment.
[0464] <Adhesive Composition>
[0465] The first piezoelectric body in the second embodiment
preferably includes an adhesive composition, from the viewpoint of
improving the piezoelectric sensitivity, and the piezoelectric
output stability.
[0466] The definition and preferred embodiments of the adhesive
composition (adhesive) in the second embodiment are the same as the
definition and preferred embodiments of the adhesive in the first
embodiment. The coating method and the physical properties of the
adhesive in the second embodiment are also the same as the coating
method and the physical properties of the adhesive in the first
embodiment.
[0467] In the coating method of the adhesive in the second
embodiment, the adhesive may be disposed, for example, after
completing the disposition of the core material and the first
piezoelectric body, between respective members (such as between the
core material and the first piezoelectric body) and at the
interfaces between the respective members and the like, in
accordance with the coating method of the adhesive in the first
embodiment, so that the respective members are adhered (bonded)
with one another.
[0468] Alternatively, the coating of the adhesive may be carried
out by coating a photocurable adhesive, a thermosetting adhesive, a
thermoplastic adhesive or the like on the surface of the first
piezoelectric body by a gravure coater, a dip coater, or the like,
in advance, followed by drying, and after completing the
disposition of the core material and the first piezoelectric body,
for example, the adhesive may be disposed between respective
members (such as between the core material and the first
piezoelectric body) and at the interfaces between the respective
members and the like, so that the respective members are adhered
(bonded) with one another.
[0469] In a case in which the non-electrically conductive core
material and the first piezoelectric body, in the piezoelectric
substrate according to the second embodiment, are twisted with each
other (for example, in the case of Specific Embodiment E), the
manner in which the core material and the first piezoelectric body
are twisted with each other is not particularly limited. However,
it is more preferred that the core material and the first
piezoelectric body are twisted with each other around the same
pivot axis and at the same number of twists.
[0470] The number of twists per 1 m of the non-electrically
conductive core material and the first piezoelectric body varies
depending on an outer diameter (thickness) of the non-electrically
conductive core material and an outer diameter (thickness) of the
first piezoelectric body. For example, in a case in which the outer
diameter of the non-electrically conductive core material and the
outer diameter of the first piezoelectric body are approximately
the same, the number of twists per 1 m is defined by the following
Equation. The definition of the "outer diameter" is the same as the
definition of the "major axis diameter of a cross section"
previously described.
[0471] Number of twists (times)=1000 (mm).times.tan
.beta.3/(.pi./D)
[0472] In the Equation, D represents the outer diameter (mm) of the
non-electrically conductive core material or the first
piezoelectric body;
.pi.D represents a circumference length of the non-electrically
conductive core material or the first piezoelectric body; and
.beta.3 represents the angle (.degree.) formed between the pivot
axis and the length direction of the first piezoelectric body.
[0473] For example, in a case in which the outer diameter of the
non-electrically conductive core material and the outer diameter of
the first piezoelectric body are approximately the same, the number
of twists per 1 m of the non-electrically conductive core material
and the first piezoelectric body is preferably represented by the
Equation: 1000 (mm).times.tan.beta.3/(.pi.D) (times) (wherein
.beta.3=45.degree..+-.30.degree.), more preferably represented by
the Equation: 1000 (mm).times.tan.beta.3/(.pi.D) (times) (wherein
.beta.3=45.degree..+-.25.degree.), still more preferably
represented by the Equation: 1000 (mm).times.tan.beta.3/(.pi.D)
(times) (wherein (.beta.3=45.degree..+-.20.degree.), and
particularly preferably represented by the Equation: 1000
(mm).times.tan.beta.3/(.pi.D) (times) (wherein
.beta.3=45.degree..+-.15.degree.), from the viewpoint of improving
the piezoelectric sensitivity and the piezoelectric output
stability as well as improving the resistance to a load such as
repeated bending or to deformation.
[0474] This allows the non-electrically conductive core material
and the first piezoelectric body to be strongly brought into close
contact with each other, and to be less susceptible to breakage
when twisted with each other, as a result of which the
piezoelectricity and the mechanical strength can be obtained in a
balanced manner.
[0475] Specifically, in a case in which the outer diameter of the
non-electrically conductive core material and the outer diameter of
the first piezoelectric body are approximately the same, the number
of twists per 1 m of the non-electrically conductive core material
and the first piezoelectric body is not particularly limited, as
long as the number of twists is within the range satisfying the
above Equation. For example, the number of twists is preferably
from 200 to 2,000 times, more preferably from 200 to 1,500 times,
still more preferably from 200 to 1,000 times, and particularly
preferably from 200 to 500 times.
[0476] In a case in which the non-electrically conductive core
material and the first piezoelectric body, in the piezoelectric
substrate according to the second embodiment, are twisted with each
other (for example, in the case of Specific Embodiment E), the
first piezoelectric body is preferably in a fibrous form composed
of a single bundle or a plurality of bundles.
[0477] The first piezoelectric body preferably has a major axis
diameter of a cross section of from 0.0001 mm to 2 mm, more
preferably from 0.001 mm to 1 mm, and still more preferably from
0.002 mm to 0.5 mm.
[0478] The definition of the "major axis diameter of a cross
section" is the same as the definition of the "major axis diameter
of a cross section" previously described.
[0479] <Method of Producing Piezoelectric Substrate>
[0480] The method of producing the piezoelectric substrate
according to the second embodiment is not particularly limited, and
the piezoelectric substrate can be produced, for example, by
preparing a first piezoelectric body, and helically winding the
first piezoelectric body in one direction with respect to a
separately prepared non-electrically conductive core material.
[0481] In a case in which the non-electrically conductive core
material and the first piezoelectric body, in the piezoelectric
substrate according to the second embodiment, are twisted with each
other, the piezoelectric substrate can be produced, for example, by
preparing the first piezoelectric body, and twisting the first
piezoelectric body and a separately prepared non-electrically
conductive core material with each other, around the same pivot
axis.
[0482] The first piezoelectric body may be one produced by a known
method, or one obtained commercially or otherwise.
[0483] In a case in which the piezoelectric substrate according to
the second embodiment includes a fiber, and the first piezoelectric
body and the fiber are formed into a braided structure, the
piezoelectric substrate can be produced by alternately crossing and
winding the first piezoelectric body and the fiber, in accordance
with the method of winding the first piezoelectric body with
respect to the non-electrically conductive core material.
[0484] Further, in a case in which the piezoelectric substrate
according to the second embodiment includes a second piezoelectric
body, and the first piezoelectric body and the second piezoelectric
body are formed into a braided structure, the piezoelectric
substrate can be produced by alternately crossing and winding the
first piezoelectric body and the second piezoelectric body in the
same manner, in accordance with the method of winding the first
piezoelectric body with respect to the non-electrically conductive
core material.
[0485] Still further, in a case in which the piezoelectric
substrate according to the second embodiment includes an electrode,
the piezoelectric substrate can be produced by disposing the
electrode by a known method.
[0486] It is to be noted that, preferably, the adhesive is used to
bind between the portions of the first piezoelectric body, and if
necessary, between the fiber and the first piezoelectric body,
between the first piezoelectric body and the second piezoelectric
body, and between the respective members included in the
piezoelectric substrate according to the second embodiment, for
example, by any of the previously described methods.
[0487] [Piezoelectric Woven Fabric]
[0488] A piezoelectric woven fabric according to the present
embodiment includes a woven fabric structure.
[0489] The woven fabric structure is composed of warp and weft
threads.
[0490] In the piezoelectric woven fabric according to the present
embodiment, at least one of the warp or weft threads include the
piezoelectric substrate according to the present embodiment
(piezoelectric substrate according to the first embodiment or the
piezoelectric substrate according to the second embodiment).
[0491] Therefore, the piezoelectric woven fabric according to the
present embodiment provides the same effect as the effect provided
by the piezoelectric substrate according to the present
embodiment.
[0492] The term "woven fabric" as used herein generally refers to a
woven fabric structure in the form of a film, obtained by crossing
threads. The term "piezoelectric woven fabric" refers, among woven
fabrics, to a woven fabric which exhibits a piezoelectric effect in
response to an external stimulus (such as a physical force).
[0493] In the piezoelectric woven fabric according to the present
embodiment, both of the warp and weft threads may include the
piezoelectric substrate according to the present embodiment.
[0494] In the case of this embodiment, it is preferred that the
first piezoelectric body included in the warp threads is wound in a
winding direction different from the winding direction of the first
piezoelectric body included in the weft threads, and the helical
chiral polymer (A) included in the warp threads has the same
chirality as the chirality of the helical chiral polymer (A)
included in the weft threads, from the viewpoint of improving the
piezoelectric sensitivity, and the piezoelectric output
stability.
[0495] Alternatively, it is preferred that the first piezoelectric
body included in the warp threads is wound in the same winding
direction as the winding direction of the first piezoelectric body
included in the weft threads, and the helical chiral polymer (A)
included in the warp threads has a chirality different from the
chirality of the helical chiral polymer (A) included in the weft
threads.
[0496] Examples of the threads include a thread containing a
polymer.
[0497] Examples of the polymer contained in the thread containing a
polymer, include: common polymers such as polyester and polyolefin,
and helical chiral polymers such as the previously described
helical chiral polymer (A).
[0498] Further, the concept of the "thread containing a polymer"
encompasses the piezoelectric substrate according to the present
embodiment.
[0499] The woven fabric structure in the piezoelectric woven fabric
according to the present embodiment is not particularly
limited.
[0500] Examples of the woven fabric structure include basic
structures such as plain weave, twill weave, and satin weave
structures.
[0501] The piezoelectric substrate according to the present
embodiment may be used as warp threads or as weft threads in the
piezoelectric woven fabric, or alternatively, as some of the warp
threads or some of the weft threads.
[0502] The piezoelectric woven fabric according to the present
embodiment may be a woven fabric having a three-dimensional
structure. The woven fabric having a three-dimensional structure
refers to a woven fabric formed into a three-dimensional object, by
additionally weaving threads (warp and weft threads) in the
thickness direction of a woven fabric having a two-dimensional
structure.
[0503] Examples of the woven fabric having a three-dimensional
structure are disclosed, for example, in JP-A No. 2001-513855.
[0504] The piezoelectric woven fabric according to the present
embodiment is not limited, as long as the piezoelectric substrate
according to the present embodiment is used as at least some of the
threads constituting the woven fabric structure.
[0505] [Piezoelectric Knitted Fabric]
[0506] A piezoelectric knitted fabric according to the present
embodiment includes a knitted fabric structure. The knitted fabric
structure includes the piezoelectric substrate according to the
present embodiment.
[0507] Accordingly, the piezoelectric knitted fabric according to
the present provides the same effect as the effect provided by the
piezoelectric substrate according to the present embodiment.
[0508] The term "knitted fabric" as used herein generally refers to
a knitted fabric obtained by knitting threads while making loops
therewith. The term "piezoelectric knitted fabric" refers, among
knitted fabrics, to a knitted fabric which exhibits a piezoelectric
effect in response to an external stimulus (such as a physical
force).
[0509] Examples of the threads include a thread containing a
polymer.
[0510] Examples of the polymer contained in the thread containing a
polymer, include: common polymers such as polyester and polyolefin,
and helical chiral polymers such as the previously described
helical chiral polymer (A).
[0511] Further, the concept of the "thread containing a polymer"
encompasses the piezoelectric substrate according to the present
embodiment.
[0512] The knitted fabric structure in the piezoelectric knitted
fabric according to the present embodiment is not particularly
limited.
[0513] Examples of the knitted fabric structure include basic
structures such as weft-knitted and warp-knitted structures.
Examples of the weft-knitted structure include those obtained by
methods such as flat knitting, rib knitting, interlock knitting,
purl knitting, and circular knitting. Examples of the warp-knitted
structure include basic structures obtained by methods such as
tricot knitting, atlas knitting, diamond knitting, and Milanese
knitting.
[0514] The piezoelectric substrate according to the present
embodiment may be used as threads in the piezoelectric knitted
fabric, or alternatively, as some of the threads.
[0515] The piezoelectric knitted fabric according to the present
embodiment may be a knitted fabric having a three-dimensional
structure. The knitted fabric having a three-dimensional structure
refers to a knitted fabric formed into a three-dimensional object,
by additionally weaving threads in the thickness direction of a
knitted fabric having a two-dimensional structure.
[0516] The piezoelectric knitted fabric according to the present
embodiment is not limited, as long as the piezoelectric substrate
according to the present embodiment is used as at least some of the
threads constituting the knitted fabric structure.
[0517] <Application of Piezoelectric Woven Fabric or
Piezoelectric Knitted Fabric>
[0518] The piezoelectric woven fabric or the piezoelectric knitted
fabric according to the present embodiment can be used in any
application which requires piezoelectricity in at least one part
thereof.
[0519] Specific examples of applications of the piezoelectric woven
fabric or the piezoelectric knitted fabric according to the present
embodiment include various types of clothing (shirts, suits,
blazers, blouses, coats, jackets, blousons, jackets, vests,
one-piece dresses, trousers, skirts, pants, underwear (slips,
petticoats, camisoles, and brassieres), socks, gloves, kimonos, obi
materials, gold brocades, cool touch clothing, ties, handkerchiefs,
mufflers, scarves, stoles, and eye masks), table clothes, footwear
(sneakers, boots, sandals, pumps, mules, slippers, ballet shoes,
and kung fu shoes), towels, pouches, bags (tote bags, shoulder
bags, handbags, pochettes, shopping bags, eco bags, rucksacks,
daypacks, sports bags, travelling bags, waist bags, waist pouches,
second bags, clutch bags, vanity bags, accessory pouches, mother's
bags, party bags, and kimono bags), pouches and cases (cosmetic
pouches, tissue cases, spectacle cases, pen cases, book covers,
pouches for gaming devices, key cases, and pass cases), wallets,
caps and hats (hats, caps, caskets, flat caps, ten-gallon hats,
floppy hats, sun visors, and berets), helmets, hoods, belts,
aprons, ribbons, corsages, broaches, curtains, wall clothes, seat
covers, sheets, comforters, comforter covers, blankets, pillows,
pillow covers, sofas, beds, baskets, various types of wrapping
materials, materials for interior decoration, automobile
accessories, imitation flowers, masks, bandages, ropes, various
types of nets, fishing nets, cement reinforcing materials, meshes
for screen printing, various types of filters (filters for
automobiles, and filters for consumer electronics), various types
of meshes, sheets (agricultural sheets, and picnic sheets), woven
fabrics for civil engineering works, woven fabrics for construction
works, and filter fabrics.
[0520] Further, the piezoelectric woven fabric or the piezoelectric
knitted fabric according to the present embodiment may be used to
constitute the entirety of any of the above described specific
examples, or alternatively, the piezoelectric woven fabric or the
piezoelectric knitted fabric according to the present embodiment
may be used only for a portion(s) thereof which need(s) to have
piezoelectricity.
[0521] The piezoelectric woven fabric or the piezoelectric knitted
fabric according to the present embodiment is particularly suitably
used in a wearable product, which is intended to be worn on a
body.
[0522] Details regarding specific embodiments of the piezoelectric
knitted fabric according to the present embodiment will be
described later, along with specific embodiments of the
piezoelectric device.
[0523] [Piezoelectric Device]
[0524] A piezoelectric device according to the present embodiment
includes the piezoelectric woven fabric according to the present
embodiment or the piezoelectric knitted fabric according to the
present embodiment.
[0525] In other words, the piezoelectric device according to the
present embodiment includes the piezoelectric substrate according
to the present embodiment or the piezoelectric woven fabric
including the piezoelectric substrate according to the present
embodiment, or alternatively, includes the piezoelectric substrate
according to the present embodiment or the piezoelectric knitted
fabric including the piezoelectric substrate according to the
present embodiment.
[0526] The piezoelectric woven fabric or the piezoelectric knitted
fabric preferably includes an electrode. The electrode is an
electrode for detecting the electric charge generated from the
piezoelectric substrate.
[0527] Electrode materials are not particularly limited, and
examples thereof include metals (such as Al). Other examples
include Ag, Au, Cu, Ag--Pd alloys, Ag pastes, Cu pastes, carbon
black, ITO (including crystalline ITO and amorphous ITO), ZnO,
IGZO, IZO (registered trademark), electrically conductive polymers
(polythiophene, PEDOT), Ag nanowires, carbon nanotubes, and
graphene.
[0528] Accordingly, the piezoelectric device according to the
present embodiment provides the same effect as the effect provided
by the piezoelectric substrate according to the present embodiment
(piezoelectric substrate according to the first embodiment or the
piezoelectric substrate according to the second embodiment).
[0529] The piezoelectric device according to the present embodiment
preferably includes: an electrode; and an insulator provided
between the electrode and the woven fabric structure or the knitted
fabric structure.
[0530] This allows for obtaining a structure in which the
occurrence of electrical short circuits between electrodes is more
easily prevented.
[0531] <Applications of Piezoelectric Substrate>
[0532] The piezoelectric substrate according to the present
embodiment (piezoelectric substrate according to the first
embodiment or the piezoelectric substrate according to the second
embodiment) can be used, for example, in sensor applications (force
sensors such as seating sensors, ultrasonic wave sensors, impact
acceleration sensors and impact sensors for use in sports goods for
various types of ball games, such as rackets, golf clubs and bats,
and the like); actuator applications (devices for sheet
transportation, and the like); energy harvesting applications
(power generation wear, power generation shoes, and the like); and
health care-related applications (wearable motion sensors obtained
by providing the sensor of the invention to various types of
clothing, such as T shirts, sportswear, spats and socks,
supporters, plaster casts, diapers, shoes, insoles for shoes,
watches, and the like).
[0533] For example, the piezoelectric woven fabric, the
piezoelectric knitted fabric, and the piezoelectric device
previously described can be used in these applications.
[0534] Among the above described applications, the piezoelectric
substrate according to the present embodiment is preferably used in
sensor applications or actuator applications.
[0535] Specifically, the piezoelectric substrate according to the
present embodiment is preferably used, mounted on a force sensor or
on an actuator.
[0536] The method of detecting the electric charge or surface
potential generated by the stress or strain in the piezoelectric
substrate according to the present embodiment include a method in
which a known non-contact surface potentiometer is used; and a
method in which an electrode made of a known electrically
conductive material is brought into proximity of the piezoelectric
substrate to be electrostatically bound to the piezoelectric
substrate, and potential changes of the electrode in this state is
read by a voltmeter or the like. Further, it is possible to use a
known extraction electrode as the electrode to be bonded. Examples
of the extraction electrode include electrode parts such as
connectors and crimp terminals. An electrode part can be bonded to
the piezoelectric substrate by brazing such as soldering, or by
using an electrically conductive bonding agent or the like.
[0537] Specific embodiments of the piezoelectric knitted fabric
according to the present embodiment will be described with
reference to the drawings.
[0538] FIG. 6 is a schematic diagram showing an example of the
piezoelectric woven fabric according to the present embodiment.
[0539] As shown in FIG. 6, a piezoelectric knitted fabric 20
according to the present embodiment includes the piezoelectric
substrate 10 and insulating threads 16, which are woven by weft
knitting, and the piezoelectric substrate 10 of Specific Embodiment
A is used as a part of the knitted fabric structure.
[0540] The piezoelectric substrate according to the present
embodiment, the piezoelectric woven fabric according to the present
embodiment, or the piezoelectric knitted fabric according to the
present is also preferably used in a device for obtaining
biological information.
[0541] In other words, a device for obtaining biological
information according to the present embodiment includes the
piezoelectric substrate according to the present embodiment, the
piezoelectric woven fabric according to the present embodiment, or
the piezoelectric knitted fabric according to the present
embodiment.
[0542] The device for obtaining biological information according to
the present embodiment is a device for detecting a biological
signal(s) of a human subject or an animal subject (hereinafter,
also collectively referred to as a "subject") by the piezoelectric
substrate, the piezoelectric woven fabric, or the piezoelectric
knitted fabric, to obtain biological information of the
subject.
[0543] Examples of the biological signal as used herein include a
pulse wave signal (heartbeat signals), a respiratory signal, a body
motion signal, a ballistocardiographic signal, and a biological
tremor.
[0544] The biological tremor refers to a rhythmical, involuntary
movement of a body part (such as a finger, hand, forearm, or upper
limb).
[0545] Further, the detection of the ballistocardiographic signal
encompasses the detection of an effect of a force due to cardiac
function of a body.
[0546] In other words, when the heart pumps blood to the aorta and
pulmonary arteries, the body receives a reactive force in the
direction opposite to the flow of the blood. The magnitude and the
direction of the reactive force change corresponding to functional
stages of the heart. The reactive force is detected by sensing the
ballistocardiographic signal outside the body.
[0547] The device for obtaining biological information is provided
and used in various types of commodities, such as for example,
various types of clothing (shirts, suits, blazers, blouses, coats,
jackets, blousons, jackets, vests, one-piece dresses, trousers,
pants, underwear (slips, petticoats, camisoles, and brassieres),
socks, gloves, kimonos, obi materials, gold brocades, cool touch
clothing, ties, handkerchiefs, mufflers, scarves, stoles, and eye
masks), supporters (neck supporters, shoulder supporters, chest
supporters, abdominal supporters, back/waist supporters, arm
supporters, leg supporters, elbow supporters, knee supporters,
wrist supporters, and ankle supporters), footwear (sneakers, boots,
sandals, pumps, mules, slippers, ballet shoes, and kung fu shoes),
insoles, towels, rucksacks, caps and hats (hats, caps, caskets,
flat caps, ten-gallon hats, floppy hats, sun visors, and berets),
helmets, chin straps for helmets, hoods, belts, seat covers,
sheets, floor cushions, cushions, comforters, comforter covers,
blankets, pillows, pillow covers, sofas, chairs, desks, tables,
sheets, seats, toilet seats, massage chairs, beds, bed pads,
carpets, baskets, masks, bandages, ropes, various types of nets,
bath tubs, flooring materials, wall materials, personal computers,
computer mice, and the like.
[0548] The device for obtaining biological information is
preferably provided and used in commodities onto which the weight
of a subject is applied, such as, for example, footwear, insoles,
sheets, floor cushions, cushions, comforters, comforter covers,
pillows, pillow covers, sofas, chairs, sheets, seats, toilet seats,
beds, carpets, bath tubs, flooring materials and the like.
[0549] An example of the operation of the device for obtaining
biological information will be described below.
[0550] The device for obtaining biological information is provided,
for example, on a bed, a seat surface of a chair, or the like. A
subject lies down, sits or stands up on top of the device for
obtaining biological information. When biological signals (such as
body motion and periodic vibrations (pulse, respiration, and the
like)) emitted from the subject in this state cause a tensile force
to be applied to the piezoelectric substrate, the piezoelectric
woven fabric, or the piezoelectric knitted fabric in the device for
obtaining biological information, polarization occurs in the
helical chiral polymer (A) included in the piezoelectric substrate,
the piezoelectric woven fabric, or the piezoelectric knitted
fabric, whereby a potential proportional to the tensile force is
generated. The potential changes overtime corresponding to the
biological signals emitted from the subject. For example, in a case
in which the biological signals emitted from the subject are
periodic vibrations, such as pulse and respiration, the potential
generated in the piezoelectric substrate, the piezoelectric woven
fabric, or the piezoelectric knitted fabric also changes
periodically.
[0551] The changes overtime in the potential generated as a result
of the application of the tensile force to the piezoelectric
substrate, the piezoelectric woven fabric, or the piezoelectric
knitted fabric are obtained as a voltage signal by a measurement
module. The thus obtained changes overtime in the potential
(piezoelectric signal) are obtained as a synthetic wave of a
plurality of biological signals (a pulse wave signal (heartbeat
signal), a respiratory signal, and a body motion signal). The
synthetic wave is separated by Fourier transformation into
respective frequencies to generate separate signals. Each of the
thus generated separate signals is subjected to inverse Fourier
transformation, to obtain respective biological signals
corresponding to the respective separate signals.
[0552] For example, in a case in which the biological signals
emitted from a subject are obtained as a synthetic wave of a
heartbeat signal and a respiratory signal, the potential generated
as a result of the application of a tensile force to the
piezoelectric substrate, the piezoelectric woven fabric, or the
piezoelectric knitted fabric in the device for obtaining biological
information, periodically changes overtime.
[0553] In general, humans have a pulse rate of from 50 to 90 times
per one minute, and a pulse frequency of from 0.6 to 3 Hz. Further,
humans generally have a respiratory rate of from 16 to 18 times per
one minute, and a respiratory frequency of from 0.1 to 1 Hz. Still
further, the frequency of body motion in humans is 10 Hz or more,
in general.
[0554] Based on such standards, a synthetic wave of a plurality of
biological signals can be separated into respective biological
signals. For example, the synthetic wave can be separated into a
respiratory signal and a heartbeat signal. Further, it is also
possible to obtain a pulse wave velocity signal from the heartbeat
signal.
[0555] The separation of a synthetic wave of a plurality of
biological signals into respective biological signals is carried
out by the Fourier transformation and inverse Fourier
transformation described above, using, for example, a biological
signal notification program.
[0556] In the above described manner, a synthetic wave of a
plurality of biological signals can be separated into a plurality
of respective biological signals.
[0557] Further, biological signal data may be produced based on at
least one of the thus separated biological signals.
[0558] The biological signal data are not particularly limited as
long as the data are calculated based on the biological signals.
Examples of the biological signal data include the number of
biological signals per unit time, and the mean value of the number
of biological signals in the past.
EXAMPLES
[0559] The present disclosure will be described more specifically
by way of Examples. However, the present disclosure is in no way
limited by the following Examples, as long as the gist of the
invention is not deviated.
[0560] <Production of Ribbon-Like Piezoelectric Body>
[0561] (Production of Slit Ribbon 1)
[0562] To 100 parts by mass of polylactic acid (product name: INGEO
(trade mark) biopolymer, brand: 4032D) manufactured by NatureWorks
LLC, as the helical chiral polymer (A), 1.0 parts by mass of a
stabilizer [a mixture of STABAXOL P400 (10 parts by mass)
manufactured by Rhein Chemie Rheinau GmbH, STABAXOL I (70 parts by
mass) manufactured by Rhein Chemie Rheinau GmbH, and CARBODILITE
LA-1 (20 parts by mass) manufactured by Nisshinbo Chemical Inc.]
was added, followed by dry blending, to prepare a raw material.
[0563] The thus prepared raw material was introduced into an
extruder hopper and extruded from a T die while heating at
210.degree. C. The resulting extrudate was brought into contact
with a cast roll controlled to 50.degree. C. for 0.3 minutes, to
form a pre-crystallized sheet having a thickness of 150 .mu.m
(pre-crystallization step). The degree of crystallinity of the
pre-crystallized sheet was measured to be 6%.
[0564] While heating the resulting pre-crystallized sheet to
70.degree. C., the stretching of the sheet was carried out in a
roll-to-roll manner at a drawing speed of 10 m/min, and the sheet
was uniaxially stretched 3.5-fold in the MD direction (stretching
step). The thus obtained film had a thickness of 49.2 .mu.m.
[0565] Subsequently, the uniaxially stretched film was subjected to
an annealing treatment, by bringing the film into contact with a
roll heated to 145.degree. C. for 15 seconds, in a roll-to-roll
manner. Then the film was rapidly cooled to prepare a piezoelectric
film (annealing treatment step).
[0566] Thereafter, the resulting piezoelectric film was slit into a
width of 0.6 mm using a slitting machine, such that the direction
of slitting was substantially parallel to the stretching direction
of the piezoelectric film. As a result, a slit ribbon 1 having a
width of 0.6 mm and a thickness of 49.2 .mu.m was obtained, as a
ribbon-like piezoelectric body. The resulting slit ribbon 1 had a
cross-sectional shape in the form of a rectangle.
[0567] (Production of Slit Ribbon 2)
[0568] The stretching step was carried out in the same manner as in
the production of the slit ribbon 1, except that the
pre-crystallized sheet was uniaxially stretched 3.4-fold in the MD
direction, to obtain a film having a thickness of 15 .mu.m.
Subsequently, the annealing treatment step was carried out in the
same manner as in the production of the slit ribbon 1, to obtain a
piezoelectric film.
[0569] Thereafter, the resulting piezoelectric film was slit into a
width of 0.2 mm using a slitting machine, such that the direction
of slitting was substantially parallel to the stretching direction
of the piezoelectric film. As a result, a slit ribbon 2 having a
width of 0.2 mm and a thickness of 15 .mu.m was obtained, as the
ribbon-like piezoelectric body. The resulting slit ribbon 2 had a
cross-sectional shape in the form of a rectangle.
[0570] <Production of Thread-Like Piezoelectric Body>
[0571] (Production of Multifilament Thread)
[0572] Polylactic acid (melting point: 170.degree. C., heat of
fusion: 38 J/g, the molar ratio of L-lactic acid/D-lactic acid:
98.5/1.5 (content of L-lactic acid: 98.5% by mole), number average
molecular weight: 85,000) was prepared as the helical chiral
polymer (A).
[0573] The polylactic acid was fed to an extrusion-type melt
spinning machine, and melt blended. The resultant was melt spun
from a spinneret, at a spinning temperature of 225.degree. C., and
the resulting thread was cooled, and an oil was applied thereto.
Thereafter, without taking up the thread once, the thread was
subjected to heat stretching by being passed between hot rollers
heated to 150.degree. C., and then taken up. As a result, a
multifilament thread (single-twisted multifilament) having a total
fineness of 295 dtex (thread count: 20, major axis diameter: 2.7
.mu.m) was obtained as a thread-like piezoelectric body. The
"single-twisted multifilament" refers to a thread obtained by
twisting a number of fibers into a single thread.
[0574] (Production of Monofilament Thread)
[0575] Polylactic acid (melting point: 170.degree. C., heat of
fusion: 38 J/g, the molar ratio of L-lactic acid/D-lactic acid:
98.5/1.5 (content of L-lactic acid: 98.5% by mole), number average
molecular weight: 85,000) was prepared as the helical chiral
polymer (A).
[0576] The polylactic acid was fed to an extrusion-type melt
spinning machine, and melt blended. The resultant was melt extruded
from a mouthpiece having a rectangular cross section, and the
resulting flat thread was cooled. Thereafter, without taking up the
thread once, the thread was heated to 70.degree. C., subjected to
heat stretching, further heated to 145.degree. C., and then taken
up. As a result, a monofilament thread (single-twisted
monofilament) having a rectangular cross section, and having a
width of 120 .mu.m and a thickness of 30 was obtained, as the
thread-like piezoelectric body.
[0577] <Measurement of Physical Properties of Ribbon-Like
Piezoelectric Body and Thread-Like Piezoelectric Body>
[0578] The physical properties of each of the ribbon-like
piezoelectric bodies and the thread-like piezoelectric bodies
obtained as described above were carried out as follows. The
results are shown in Table 1.
[0579] <Degree of Orientation F of Polylactic Acid>
[0580] Using a wide-angle x-ray diffraction apparatus (RINT 2550,
manufactured by Rigaku Corporation; accessory device: rotary sample
stand, X-ray source: CuK.alpha., output: 40 kV 370 mA, detector:
scintillation counter), each sample (the ribbon-like piezoelectric
body or the thread-like piezoelectric body) was fixed to a holder,
and an azimuthal distribution intensity of a crystal plane peak
[(110) plane/(200) plane] was measured.
[0581] From the degree of crystallinity and the half-value width
(.alpha.) of the peak in the resulting azimuthal distribution curve
(X-ray interference diagram), the degree of orientation F (degree
of orientation of C axis) of the polylactic acid was calculated
according to the following Equation, and then evaluated.
Degree of orientation (F)=(180.degree.-.alpha.)/180.degree.
(In the Equation, a represents the half-value width of the peak
derived from the orientation.)
TABLE-US-00001 TABLE 1 Type of Degree of Degree of Piezoelectric
body Material Form crystallinity orientation F Ribbon-like Slit
Polylactic Slit 45% 0.97 piezo- ribbon 1 acid ribbon 46% 0.97
electric Slit body ribbon 2 Thread- Multi- Polylactic Thread 56%
0.81 like filament acid piezo- thread electric Mono- 57% 0.96 body
filament threadn
Example 1
[0582] <Production of Piezoelectric Substrate>
[0583] A piezoelectric substrate having the same configuration as
the piezoelectric substrate 10 shown in FIG. 1, namely, the
piezoelectric substrate 10 including no core material, was prepared
by the method shown below.
[0584] The thread-like piezoelectric body (single-twisted
multifilament thread) obtained as described above was helically
wound (twined) in the left-handed direction with respect to a
virtual helical axis, such that the piezoelectric body was oriented
in a direction of 45.degree. with respect to the helical axis (at a
helix angle of 45.degree.), and that no gap is formed. The helical
axis corresponds to the central axis of a helical structure formed
with the thread-like piezoelectric body. The thread-like
piezoelectric body was visually observed by a stereoscopic
microscope, to confirm that the number of twists was about 10 turns
per 10 mm. Accordingly, the number of twists per 1 m of the present
Example was determined to be 1,000 turns (1,000 T/m). The
expression "wound in the left-handed direction" means that, when
the piezoelectric body is seen from one end of the helical axis (on
the right side, in the case of FIG. 1), the thread-like
piezoelectric body is wound from the near side to the far side in
the left-handed (anti-clockwise) direction.
[0585] In the above described manner, a piezoelectric substrate of
Example 1 was obtained. The thread-like piezoelectric body
corresponds to the first piezoelectric body 14A shown in FIG. 1.
The helical axis corresponds to G1 shown in FIG. 1.
[0586] <Evaluation>
[0587] (Surface Potential Generated Per Unit Tensile Force)
[0588] The piezoelectric substrate of Example 1 was used as a
sample, and the sample was set on a tensile tester (TENSILON RTG
1250, manufactured by A&D Company, Limited) at a chuck-to-chuck
distance of 50 mm.
[0589] Using the tensile tester, a tensile force was repeatedly
applied to the sample, within a stress range of from 1.0 N to 2.0 N
in a periodic manner and in the form of a triangular wave, and the
surface potentials generated on both sides of the sample at this
time were measured by a surface potentiometer (MODEL 541A-2,
manufactured by TREK Inc.).
[0590] The measurement was carried out in an arrangement in which a
sensor head of the surface potentiometer was disposed at a central
portion between the chucks of the tensile tester, and the sensor
head was brought into a proximity of 2 mm to the linear
piezoelectric substrate to be measured, such that a normal line of
a circular end surface of the cylinder-shaped sensor head was
orthogonal to the piezoelectric substrate.
[0591] Further, the measurement sample and the chuck portion of the
tensile tester were surrounded by an aluminum metal plate to be
electrostatically shielded, and the aluminum metal plate and a
ground electrode of the surface potentiometer were electrically
connected, to carry out the measurement.
[0592] The measured surface potential difference .DELTA.V [V] was
plotted on Y axis, and the tensile force F [N] of the sample was
plotted on X axis to obtain a scatter diagram, and the surface
potential generated per unit tensile force was calculated from the
slope of a correlation line in the scatter diagram, and taken as a
voltage sensitivity (force-voltage sensitivity) with respect to the
applied force (tensile force) [V/N]. The result is shown in Table
2. The value of the force-voltage sensitivity shown in Table 2 is
an absolute value.
[0593] Regarding the force-voltage sensitivity, it is to be noted
that the value of the amount of change in the surface potential as
measured by a surface potentiometer when the tensile force was
increased, in the piezoelectric substrate wound in the right-handed
direction, has a positive/negative sign opposite from the sign of
the corresponding value in the piezoelectric substrate wound in the
left-handed direction, because of the relationship between a
mechanism by which the helical chiral polymer exhibits
piezoelectricity and the winding direction. Accordingly, in the
present Example, the value of the force-voltage sensitivity is a
negative value.
Example 2
[0594] A piezoelectric substrate having the same configuration as
the piezoelectric substrate 10B shown in FIG. 3 was produced by the
method shown below.
[0595] First, a meta aramid fiber, CORNEX (yarn count: 40, wire
diameter: 0.12 mm, length: 200 mm, double-twisted) manufactured by
Teijin Limited was prepared, as a core material.
[0596] Subsequently, the thread-like piezoelectric body
(single-twisted multifilament thread) obtained as described above
was helically wound around the double-twisted core material in the
left-handed direction, such that the piezoelectric body was
oriented in a direction of 45.degree. (helix angle: 45.degree.)
with respect to the axial direction of the core material (helical
axis direction), and that no gap was formed not to expose the core
material from between the wound piezoelectric body, thereby
including the core material inside the piezoelectric body. The
expression "wound in the left-handed direction" means that, when
the piezoelectric body is seen from one end of the axial direction
of the core material (on the right side, in the case of FIG. 3),
the thread-like piezoelectric body is wound from the near side to
the far side of the core material in the left-handed direction. For
the winding, a covering apparatus used to produce lame threads for
use in decorative clothing and the like, was used.
[0597] In the above described manner, a piezoelectric substrate of
Example 2 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
[0598] The core material corresponds to the core material 12A shown
in FIG. 3. The thread-like piezoelectric body corresponds to the
first piezoelectric body 14A shown in FIG. 3. The helical axis
corresponds to G3 shown in FIG. 3.
Example 3
[0599] A piezoelectric substrate having the same configuration as
the piezoelectric substrate of Example 2 was prepared, except that
the thread-like piezoelectric body was changed to the material
shown below.
[0600] A meta aramid fiber, CORNEX (yarn count: 40, wire diameter:
0.12 mm, length: 200 mm, double-twisted) manufactured by Teijin
Limited was prepared, as a core material. Then the ribbon-like
piezoelectric body obtained as described above (slit ribbon 1), and
having a width of 0.6 mm and a thickness of 49.2 .mu.m, was
helically wound around the core material in the left-handed
direction, such that the piezoelectric body was oriented in a
direction of 45.degree. (helix angle: 45.degree.) with respect to
the axial direction of the core material (helical axis direction),
and that no gap was formed not to expose the core material from
between the wound piezoelectric body, thereby including the core
material inside the piezoelectric body.
[0601] In the above described manner, a piezoelectric substrate of
Example 3 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 4
[0602] A piezoelectric substrate was prepared in the same manner as
in Example 1, except that ARON ALPHA 201 (a cyanoacrylate adhesive)
manufactured by Toagosei Co., Ltd. was applied dropwise onto the
thread-like piezoelectric body of the piezoelectric substrate
obtained in Example 1, to be impregnated thereinto, followed by
curing the ARON ALPHA 201.
[0603] In the above described manner, a piezoelectric substrate of
Example 4 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 5
[0604] A piezoelectric substrate was prepared in the same manner as
in Example 2, except that ARON ALPHA 201 (a cyanoacrylate adhesive)
manufactured by Toagosei Co., Ltd. was applied dropwise onto the
thread-like piezoelectric body of the piezoelectric substrate
obtained in Example 2, to be impregnated thereinto, followed by
curing the ARON ALPHA 201.
[0605] In the above described manner, a piezoelectric substrate of
Example 5 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 6
[0606] A piezoelectric substrate was prepared in the same manner as
in Example 3, except that ARON ALPHA 201 (a cyanoacrylate adhesive)
manufactured by Toagosei Co., Ltd. was applied dropwise onto the
ribbon-like piezoelectric body of the piezoelectric substrate
obtained in Example 3, to be impregnated thereinto, followed by
curing the ARON ALPHA 201.
[0607] In the above described manner, a piezoelectric substrate of
Example 6 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 7
[0608] The ribbon-like piezoelectric body obtained as described
above (slit ribbon 1), and having a width of 0.6 mm and a thickness
of 49.2 .mu.m, was subjected to twisting processing in the
right-handed direction at 1,540 turns (1540 T/m) per 1 m, without
using any core material, to be formed into the shape of a hollow
tube. In order to integrate the resulting tube, ARON ALPHA 201 (a
cyanoacrylate adhesive) manufactured by Toagosei Co., Ltd. was
applied dropwise on the tube to be impregnated thereinto, thereby
integrating the tube. In the above described manner, a
piezoelectric substrate of Example 7 was produced, and the
evaluation was carried out in the similar manner as in Example 1.
However, in the evaluation, the chuck-to-chuck distance was changed
as shown in Table 2. The result is shown in Table 2.
[0609] In the following Example 8 to Example 11, piezoelectric
substrates were prepared in accordance with the method of Example
2, using the core materials and the materials for piezoelectric
bodies shown in Table 2, and based on the winding direction of the
piezoelectric bodies shown in Table 2.
Example 8
[0610] First, five pieces of heat fusible Nylon fibers, ELDER
(330T-102-EL94) manufactured by Toray Industries, Inc. were formed
into a bundle, to be used as a core material.
[0611] Subsequently, the ribbon-like piezoelectric body obtained as
described above (slit ribbon 1), and having a width of 0.6 mm and a
thickness of 49.2 .mu.m, was helically wound around the core
material in the right-handed direction, such that the piezoelectric
body was oriented in a direction of 45.degree. (helix angle:
45.degree.) with respect to the axial direction of the core
material (helical axis direction), and that no gap was formed not
to expose the core material from between the wound piezoelectric
body, thereby including the core material inside the piezoelectric
body.
[0612] Further, in order to melt the heat fusible Nylon fibers
(hereinafter, also referred to as "heat fusible fibers") and to
integrate the piezoelectric body by adhesion, the resultant was
placed in an oven controlled to 120.degree. C. and heated for 15
minutes, to be melt-integrated.
[0613] In the above described manner, a piezoelectric substrate of
Example 8 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 9
[0614] First, three pieces of polyester threads (multifilament
threads, 40 deniers) manufactured by Toray Industries, Inc. were
formed into a bundle, to be used as a core material.
[0615] Subsequently, the thread-like piezoelectric body
(monofilament thread) obtained as described above, and having a
width of 120 .mu.m and a thickness of 30 was helically wound around
the core material in the left-handed direction, such that the
piezoelectric body was oriented in a direction of 45.degree. (helix
angle: 45.degree.) with respect to the axial direction of the core
material (helical axis direction), and that no gap was formed not
to expose the core material from between the wound piezoelectric
body, thereby including the core material inside the piezoelectric
body.
[0616] In the above described manner, a piezoelectric substrate of
Example 9 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 10
[0617] First, three pieces of polyester threads (multifilament
threads, 40 deniers) manufactured by Toray Industries, Inc. were
formed into a bundle, to be used as a core material. The
ribbon-like piezoelectric body obtained as described above (slit
ribbon 2), and having a width of 0.2 mm and a thickness of 15 was
helically wound around the core material in the left-handed
direction, such that the piezoelectric body was oriented in a
direction of 45.degree. (helix angle: 45.degree.) with respect to
the axial direction of the core material (helical axis direction),
and that no gap was formed not to expose the core material from
between the wound piezoelectric body, thereby including the core
material inside the piezoelectric body.
[0618] In the above described manner, a piezoelectric substrate of
Example 10 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
Example 11
[0619] First, three pieces of polyester threads (multifilament
threads, 40 deniers) manufactured by Toray Industries, Inc. were
formed into a bundle, to be used as a core material. Subsequently,
one piece of heat fusible Nylon fiber, ELDER (330T-102-EL94, 297
deniers) manufactured by Toray Industries, Inc. was helically wound
around the core material, to include the core material inside the
heat fusible fiber. The ribbon-like piezoelectric body obtained as
described above (slit ribbon 2), and having a width of 0.2 mm and a
thickness of 15 .mu.m, was helically wound in the left-handed
direction around the core material on the surface of which the heat
fusible fiber had been wound, such that the piezoelectric body was
oriented in a direction of 45.degree. (helix angle: 45.degree.)
with respect to the axial direction of the core material (helical
axis direction), and that no gap was formed not to expose the core
material from between the wound piezoelectric body, thereby
including the core material inside the piezoelectric body. Further,
in order to melt the heat fusible fiber so that the piezoelectric
body and the core material are adhered with each other and
integrated, the resultant was placed in an oven controlled at
120.degree. C. for 15 minutes.
[0620] In the above described manner, a piezoelectric substrate of
Example 11 was produced, and the evaluation was carried out in the
similar manner as in Example 1. However, in the evaluation, the
chuck-to-chuck distance was changed as shown in Table 2. The result
is shown in Table 2.
[0621] (Tensile Elastic Modulus of Cured Product of Adhesive)
[0622] Using the adhesive (a cyanoacrylate adhesive) used in the
production of the piezoelectric substrate of Example 4, the tensile
elastic modulus of a cured product of the adhesive was measured, in
accordance with ASTM D-882. As a result, the measured tensile
elastic modulus was 330 MPa. The measurement method was as
follows.
[0623] A sheet made of water-soluble polyvinyl alcohol (PVA) was
used to prepare a vat having a depth of 0.5 mm, a short side length
of 30 mm, and a long side length of 80 mm. The adhesive was poured
into the vat and then cured. After the curing, the sheet made of
water-soluble PVC was removed by being dissolved in water, to
obtain a test specimen of a cured product of the adhesive in the
shape of a strip. The strip-shaped test specimen was set on a
tensile tester (TENSILON RTG 1250 manufactured by A&D Company,
Limited) at a chuck-to-chuck distance of 50 mm. Using the tensile
tester, a tensile force was repeatedly applied to the sample,
within the stress range of from 1.0 N to 2.0 N in a periodic manner
in the form of a triangular wave, and the strain of the
strip-shaped test specimen of the cured product of the adhesive was
measured. Then the tensile elastic modulus was calculated from the
measured result.
TABLE-US-00002 TABLE 2 Piezoelectric body Evaluation Degree of
Chuck-to- Force- Winding orientation chuck distance piezoelectric
Core material Material Form direction F Adhesive [mm] sensitivity
[V/N] Example -- Polylactic Multifilament thread Left 0.81 -- 50
0.19 1 acid (yarn count: 20, single twisted .times. 1 piece)
Example Meta-aramid fiber Polylactic Multifilament thread Left 0.81
-- 70 0.13 2 (yarn count: 40, double acid (yarn count: 20, twisted
.times. 1 piece) single twisted .times. 1 piece) Example
Meta-aramid fiber Polylactic Slit ribbon 1 Left 0.97 -- 80 1.4 3
(yarn count: 40, double acid (width: 0.6 mm, twisted .times. 1
piece) thickness: 49.2 .mu.m) Example -- Polylactic Multifilament
thread Left 0.81 Used 70 3.5 4 acid (yarn count: 20, (ARON single
twisted .times. 1 piece) ALPHA 201) Example Meta-aramid fiber
Polylactic Multifilament thread Left 0.81 Used 70 6.3 5 (yarn
count: 40, double acid (yarn count: 20, (ARON twisted .times. 1
piece) single twisted .times. 1 piece) ALPHA 201) Example
Meta-aramid fiber Polylactic Slit ribbon 1 Left 0.97 Used 80 13 6
(yarn count: 40, double acid (width: 0.6 mm, (ARON twisted .times.
1 piece) thickness: 49.2 .mu.m) ALPHA 201) Example -- Polylactic
Slit ribbon 1 Right 0.97 Used 100 12 7 acid (width: 0.6 mm, (ARON
thickness: 49.2 .mu.m) ALPHA 201) Example Heat fusible nylon fibers
Polylactic Slit ribbon 1 Right 0.97 Used 100 7.8 8 (297 denier
.times. 5 pieces) acid (width: 0.6 mm, (Heat fusible thickness:
49.2 .mu.m) fibers, 5 pieces) Example Polyester threads Polylactic
Monofilament thread Left 0.96 -- 100 1.2 9 (40 denier .times. 3
pieces) acid (width: 120 .mu.m, thickness: 30 .mu.m) Example
Polyester threads Polylactic Slit ribbon 2 Left 0.97 -- 100 2.6 10
(40 denier .times. 3 pieces) acid (width: 0.2 mm, thickness: 15
.mu.m) Example Polyester threads Polylactic Slit ribbon 2 Left 0.97
Used 100 4.8 11 (40 denier .times. 3 pieces) acid (width: 0.2 mm,
(Heat fusible thickness: 15 .mu.m) fiber, 1 piece)
[0624] Each of the piezoelectric substrates produced in Examples 1,
4, and 7 includes a piezoelectric body helically wound in one
direction with respect to a virtual helical axis, and does not
include a core material. Each of the piezoelectric substrates
produced in Examples 2, 3, 5, 6, and 8 to 11 includes a core
material, and a piezoelectric body helically wound in one direction
with respect to the core material.
[0625] It can be seen from Table 2 that, in the piezoelectric
substrates of Examples 1 to 11, surface potentials were generated
by the application of a tensile force thereto, and each of the
piezoelectric substrates has a favorable "force-voltage
sensitivity", namely, has piezoelectricity.
[0626] This is thought to be because, since the arrangement
direction of the piezoelectric body (the length direction of the
piezoelectric body) with respect to the helical axis is
substantially parallel to the main direction of orientation of the
helical chiral polymer (A), in each of the piezoelectric substrates
of Examples 1 to 11, polarization was effectively generated in the
helical chiral polymer (A) included in the piezoelectric body, by
the application of a tensile force to the piezoelectric
substrate.
[0627] In particular, the above results have revealed that the
piezoelectric substrates of Examples 4 to 6, in which the
piezoelectric bodies were impregnated with an adhesive, have a
higher "force-voltage sensitivity" as compared to the piezoelectric
substrates of Examples 1 to 3, in which the piezoelectric bodies
were not impregnated with the adhesive. This is probably because,
since adjacent portions of the piezoelectric body are adhered with
each other by the adhesive, in each of the piezoelectric substrates
of Examples 4 to 6, the transmission of the tensile force to the
piezoelectric body is facilitated, resulting in a more effective
generation of polarization in the helical chiral polymer (A).
[0628] Further, the piezoelectric substrate of Example 11, in which
the piezoelectric body and the core material are adhered and
integrated with each other by a heat fusible fiber, has a higher
"force-voltage sensitivity" as compared to the piezoelectric
substrate of Example 10, in which the piezoelectric body and the
core material are not adhered and integrated with each other. This
is thought to be because the interposition of the adhesive prevents
the displacement between the piezoelectric body and the core
material, and facilitates the transmission of the tensile force
applied to the piezoelectric substrate, resulting in an increase in
the shear stress transmitted to the piezoelectric body.
[0629] It is to be noted that, in a piezoelectric substrate
including an electrically conductive core material as a core
material, the metal conductor portion of the electrically
conductive core material tends to be susceptible to breakage due to
fatigue, as a result of the application of a load, such as repeated
bending. However, since the piezoelectric substrates of Examples 1
to 11 include no core material (Examples 1, 4, and 7), or include a
non-electrically conductive core material as a core material
(Examples 2, 3, 5, 6, and 8 to 11), it has been suggested that the
breakage due to fatigue is reduced and the resistance to a load,
such as repeated bending or to deformation, is improved in the
piezoelectric substrates of Examples 1 to 11, as compared to the
piezoelectric substrate including an electrically conductive core
material.
[0630] The disclosure of Japanese Patent Application No.
2016-113011 filed on Jun. 6, 2016, is incorporated herein by
reference in their entirety.
[0631] All publications, patent applications, and technical
standards mentioned in the present specification are incorporated
herein by reference to the same extent as if such individual
publication, patent application, or technical standard was
specifically and individually indicated to be incorporated by
reference.
* * * * *